Notes on the Troubleshooting and Repair of Audio Equipment and Other Miscellaneous Stuff

Version 3.50 (17-Apr-09)

Copyright © 1994-2010
Samuel M. Goldwasser
--- All Rights Reserved ---

For contact info, please see the
Sci.Electronics.Repair FAQ Email Links Page.


Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:
  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.



Table of Contents



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Preface

    Author and Copyright

    Author: Samuel M. Goldwasser

    For contact info, please see the Sci.Electronics.Repair FAQ Email Links Page.

    Copyright © 1994-2010
    All Rights Reserved

    Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

    1. This notice is included in its entirety at the beginning.
    2. There is no charge except to cover the costs of copying.

    DISCLAIMER

    Although working on small audio and related electronic equipment is generally less risky than dealing with equipment like microwave ovens, TVs, and computer monitors, devices that plug into the wall can still produce a very lethal electric shock as well cause a fire from incorrect or careless repairs both during servicing or later on. It is essential that you read, understand, and follow all safety guidelines contained in this document and in the document: Safety Guidelines for High Voltage and/or Line Powered Equipment.

    Improper repair of battery operated devices can also result in bad consequences for you, the device, and any equipment attached to it.

    We will not be responsible for damage to equipment, your ego, county wide power outages, spontaneously generated mini (or larger) black holes, planetary disruptions, or personal injury or worse that may result from the use of this material.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Introduction

    Note: Information on AC adapters, power supplies, batteries, and electronic flash units has been relocated to other documents (with what should be obvious titles) in this same directory.

    Why is all that junk in your attic?

    If you have ever tried to get a piece of consumer electronic equipment repaired, you understand why so much dead stuff is likely to be gathering dust in your attic or basement closet or junk box. It does not pay! This may be partially by design. However, to be fair, it may take just as much time to diagnose and repair a problem with a $20 Walkman as a $300 VCR and time is money for a repair shop. It is often not even economical to repair the more expensive equipment let alone a $40 answering machine. The cost of the estimate alone would probably buy at least one new unit and possibly many more.

    However, if you can do the repair yourself, the equation changes dramatically as your parts costs will be 1/2 to 1/4 of what a professional will charge and of course your time is free. The educational aspects may also be appealing. You will learn a lot in the process. Many problems can be solved quickly and inexpensively. Fixing an old boombox to take take to the beach may just make sense after all.

    This document provides maintenance and repair information for a variety of consumer electronic devices not covered by other documents in the "Notes on the Troubleshooting and Repair of..." series. Suggestions for additions (and, of course, correction) are always welcome.

    You will be able to diagnose problems and in most cases, correct them as well. As most difficulties encountered with this type of equipment are mechanical, there is significant emphasis on dirt, lubrication, deteriorated rubber parts, broken doohickies, and so forth. With minor exceptions, specific manufacturers and models will not be covered as there are so many variations that such a treatment would require a huge and very detailed text. Rather, the most common problems will be addressed and enough basic principles of operation will be provided to enable you to narrow the problem down and likely determine a course of action for repair - or decide that replacement is indeed the better option. However, in many cases, you will be able to do what is required to repair a piece of equipment for a fraction of what would be charged by a repair center. Perhaps, you will even be able to revive something that would otherwise have gone into the dumpster - or remained in that closet until you moved out of your house (or longer)!

    Should you still not be able to find a solution, you will have learned a great deal and be able to ask appropriate questions and supply relevant information if you decide to post to sci.electronics.repair. It will also be easier to do further research using a repair book or guide. In any case, you will have the satisfaction of knowing you did as much as you could before finally giving up or (if it is worthwhile cost-wise) taking it in for professional repair. With your new-found knowledge, you will have the upper hand and will not easily be snowed by a dishonest or incompetent technician.

    If you are just getting started, you should refer to "Repair Briefs, an Introduction" for additional troubleshooting tips, recommended test equipment, suggested parts inventory, and other general information.

    Information on consumer electronics technology

    Your local public library (621.384 if your library is numbered that way) or technical bookstore represents a valuable resource for books on both the technology and repair of a large variety of consumer electronics devices.

    For general troubleshooting techniques, see the section: Some general references.

    The How Stuff Works Web site has some really nice introductory material (with graphics) on a variety of topics relating to technology in the modern world. Of relevance to this document are articles on motors, power adapters, relays, batteries, etc.

    Check out "Sam's Neat, Nifty, and Handy Bookmarks" (at this site) in the "Education and Tutorials" area for links to basic introductory material on electronics and other related fields.

    Web sites dealing with low voltage wiring

    This site deals with non-power wiring information: phones, audio, video, home automation, etc. Since much of the content of this document relates to home electronics that may involve such wiring, it may be of interest.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Maintenance and Troubleshooting Guide

    SAFETY

    The only danger to you in most audio equipment and the other devices covered in this document is from the AC line connection (if any) and getting sucked into any mechanical people traps. Before you plug in the unit with any covers removed, make note and cover up any exposed AC line connections. The rest of the circuitry is low voltage and while you can destroy your equipment by your actions, you should be fairly safe. Exceptions to this are noted where appropriate.

    Getting zapped from a piece of audio (or other A/V) equipment

    A slight (or not so slight) tingle when touching cabinet parts, or even a sort of vibration not due to actual physical movement as you run a finger over the metal may be an indication of some electrical leakage. Usually, this is harmless but can probably be eliminated.

    Check with a multimeter on the AC volts range between any combination of user accessible parts - cases, antenna jacks, etc., and an earth ground like the third hole of a properly grounded outlets.

    Troubleshooting tips

    Many problems have simple solutions. Don't immediately assume that your problem is some combination of esoteric complex convoluted failures. For a tape deck, it may just be a bad belt or a bad tape. Try to remember that the problems with the most catastrophic impact on operation (a dead AC adapter) have the simplest solutions (repair the wires broken due to flexing in the power cable).

    If you get stuck, sleep on it. Sometimes, just letting the problem bounce around in your head will lead to a different more successful approach or solution. Don't work when you are really tired - it is both dangerous and mostly non-productive (or possibly destructive).

    Whenever working on precision equipment, make copious notes and diagrams. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange of cables, but not always. Apparently identical screws may be of differing lengths or have slightly different thread types. Little parts may fit in more than one place or orientation. Etc. Etc.

    Pill bottles, film canisters, and plastic ice cube trays come in handy for sorting and storing screws and other small parts after disassembly.

    Select a work area which is well lighted and where dropped parts can be located - not on a deep pile shag rug. Something like a large plastic tray with a slight lip may come in handy as it prevents small parts from rolling off of the work table. The best location will also be relatively dust free and allow you to suspend your troubleshooting to eat or sleep or think without having to pile everything into a cardboard box for storage.

    Another consideration is ESD - Electro-Static Discharge. The electronic components in a some devices like cassette decks, Walkmen, and portable phones, are vulnerable to ESD. There is no need to go overboard but taking reasonable precautions like not wearing clothing made of wool that tends to generate static. When working on larger devices like cassette decks, get into the habit of touching a ground like the metal chassis before touching any circuit components.

    A basic set of precision hand tools will be all you need to disassemble and perform adjustments on most consumer electronic equipment. These do not need to be really expensive but poor quality tools are worse than useless and can cause damage. Needed tools include a selection of Philips and straight blade screwdrivers, needlenose pliers, wire cutters, tweezers, and dental picks. A jeweler's screwdriver set is a must particularly if you are working on compact equipment. For adjustments, a miniature (1/16" blade) screwdriver with a non-metallic tip is desirable both to prevent the presence of metal from altering the electrical properties of the circuit and to minimize the possibility of shorting something from accidental contact with the circuitry.

    For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller' (they are the same) and a heat gun or blow dryer come in handy to identify components whose characteristics may be drifting with temperature. Using the extension tube of the spray can or making a cardboard nozzle for the heat gun can provide very precise control of which components you are affecting.

    Basic cleaning supplies include Q-tips (you may know them as cotton buds) for everything BUT the video heads on VCRs and other helical scan tape transports, chamois covered cleaning sticks (for video heads), lint free cloths or paper towels, water, and isopropyl alcohol (preferably 91 percent medicinal grade or better).

    For info on useful chemicals, adhesives, and lubricants, see "Repair Briefs, an Introduction" as well as other documents available at this site.

    Soldering equipment

    The ease and quality of your work will depend both on proper soldering as well as desoldering (often called rework) equipment.

    Three wire grounded soldering equipment is recommended but I do not consider it essential for this type of repair work. However, a temperature regulated soldering station is a really nice piece of equipment if you can afford it or happen on a really good deal.

    I consider fine gauge rosin core solder (.030 or less) to be best for most applications (e.g., Ersin Multicore).

    CAUTION: You can easily turn a simple repair (e.g., bad solder connections) into an expensive mess if you use inappropriate soldering equipment and/or lack the soldering skills to go along with it. If in doubt, find someone else to do the soldering or at least practice, practice, practice, soldering and desoldering on a junk circuit board first!

    Soldering techniques

    Soldering is a skill that is handy to know for many types of construction and repair. For modern small appliances, it is less important than it once was as solderless connectors have virtually replaced solder for internal wiring.

    However, there are times where soldering is more convenient. Use of the proper technique is critical to reliability and safety. A good solder connection is not just a bunch of wires and terminals with solder dribbled over them. When done correctly, the solder actually bonds to the surface of the metal (usually copper) parts.

    Effective soldering is by no means difficult but some practice may be needed to perfect your technique.

    The following guidelines will assure reliable solder joints:

    Practice on some scrap wire and electronic parts. It should take you about 3 minutes to master the technique!

    Desoldering techniques

    Occasionally, it will be necessary to remove solder - either excess or to replace wires or components. A variety of tools are available for this purpose. The one I recommend is a vacuum solder pump called 'SoldaPullet' (about $20). Cock the pump, heat the joint to be cleared, and press the trigger. Molten solder is sucked up into the barrel of the device leaving the terminal nearly free of solder. Then use a pair of needlenose pliers and a dental pick to gently free the wires or component. Other approaches that may be used in place of or in addition to this: Solder Wick which is a copper braid that absorbs solder via capillary action; rubber bulb type solder pumps, and motor driven vacuum solder rework stations (pricey).

    See the document: Troubleshooting and Repair of Consumer Electronics Equipment for additional info on desoldering of electronic components.

    Soldering pins in plastic connectors

    The thermoplastic used to mold many common cheap connectors softens or melts at relatively low temperatures. This can result in the pins popping out or shifting position (even shorting) as you attempt to solder to them to replace a bad connection, for example.

    One approach that works in some cases is to use the mating socket to stabilize the pins so they remain in position as you solder. The plastic will still melt - not as much if you use an adequately sized iron since the socket will act as a heat sink - but will not move.

    An important consideration is using the proper soldering iron. In some cases, a larger iron is better - you get in and out more quickly without heating up everything in the neighborhood.

    Test equipment

    Don't start with the electronic test equipment, start with some analytical thinking. Many problems associated with consumer electronic equipment do not require a schematic (though one may be useful). The majority of problems with consumer electronic equipment are mechanical and can be dealt with using nothing more than a good set of precision hand tools; some alcohol, degreaser, contact cleaner, light oil and grease; and your powers of observation (and a little experience). Your built in senses and that stuff between your ears represents the most important test equipment you have.

    A DMM or VOM is necessary for checking of power supply voltages and testing of sensors, LEDs, switches, and other small components. This does not need to be expensive but since you will be depending on its readings, reliability is important. Even a relatively inexpensive DMM from Radio Shack will be fine for most repair work. You will wonder how you ever lived without one! Cost: $25-50.

    Unless you get deep into electronic repair, a high bandwidth oscilloscope is not required. However, a relatively inexpensive 5 or 10 MHz dual trace scope is very handy and you will find all kinds of uses for it. Such a scope should cost less than $150 on the used market.

    There are several specific pieces of test equipment that you may already own which are required depending on the devices being fixed.

    Audio equipment:

    Video games, cable boxes, and other video sources:

    Telephone equipment:

    Handy-dandy phone line tester

    This simple device (total cost about $3) will show at a glance the status of all of the phone lines connected to a modular jack.

    Parts list:

    For each phone line:

    Construct the following circuit for each line and attach to the appropriate color terminals/wires of the modular jack:

    
                               10K            Green LED
    Line 1:     (Green) o------/\/\-----+--------|>|-------+------o (Red
    Line 2:     (Black)                 |  Wiring Correct  |        (Yellow)
    Line 3:     (White)                 |                  |        (Blue)
                                        |      Red LED     |
                                        +--------|<|-------+
                                         Reverse Polarity
    
    

    Note: Polarity of Tip and Ring are reversed with respect to the wire colors because of swap that occurs using the RJ11 extension cord.

    Mount the LEDs in holes drilled in the plastic cover of the modular jack (making sure they clear the base when the cover is screwed down).

    To test old style 4 prong phone jacks, use an adapter on the end of the RJ11 extension cord.

    Correctly wired lines will light up green, reverse polarity will be red, dead line will be dark, line-in-use will be dark or nearly dark. If you catch a line that is ringing. both LEDs will flicker.

    Putting just the LED portion (leave out the resistor) of this circuit in *series* with the phone line will implement an off-hook (in use) indicator.

    Getting inside consumer electronic equipment

    Yes, you will void the warranty, but you knew this already.

    Note: the sections on loudspeakers, cameras, and watches have additional 'getting inside' info.

    Manufacturers seem to take great pride in being very mysterious as to how to open their equipment. Not always, but this is too common to just be a coincidence.

    A variety of techniques are used to secure the covers on consumer electronic equipment:

    1. Screws. Yes, many still use this somewhat antiquated technique. Sometimes, there are even embossed arrows on the case indicating which screws need to be removed to get at the guts. In addition to obvious screw holes, there may be some that are only accessible when a battery or cassette compartment is opened or a trim panel is popped off.

      These will often be of the Philips variety. (Strictly speaking, many of these are not actual Philips head screws but a slight variation. Nonetheless, a Philips screwdriver of suitable size will work on them.) A precision jeweler's screwdriver set including miniature Philips head drivers is a must for repair of miniature portable devices.

      Sometimes, you will find Torx or a variety of security type fasteners. Suitable driver bits are available. Sometimes, you can improvise using regular tools. In the case of security Torx, the center post can usually be broken off with a pair of needlenose pliers allowing a normal Torx driver to be used. In a pinch, a suitable size hex wrench can substitute for a Torx driver. Places like MCM Electronics carry a variety of security bits.

    2. Hidden screws. These will require prying up a plug or peeling off a decorative decal. It will be obvious that you were tinkering - it is virtually impossible to put a decal back in an undetectable way. Sometimes the rubber feet can be pryed out revealing screw holes. For a stick-on label, rubbing your finger over it may permit you to locate a hidden screw hole. Just puncture the label to access the screw as this may be less messy then attempting to peel it off.

    3. Snaps. Look around the seam between the two halves. You may (if you are lucky) see points at which gently (or forcibly) pressing with a screwdriver will unlock the covers. Sometimes, just going around the seam with a butter knife will pop the cover at one location which will then reveal the locations of the other snaps.

    4. Glue. Or more likely, the plastic is fused together. This is particularly common with AC adapters (wall warts). In this case, I usually carefully go around the seam with a hacksaw blade taking extreme care not to go through and damage internal components. Reassemble with plastic electrical tape.

    5. It isn't designed for repair. Don't laugh. I feel we will see more and more of this in our disposable society. Some devices are totally potted in Epoxy and are throwaways. With others, the only way to open them non-destructively is from the inside.

    Don't force anything unless you are sure there is no alternative - most of the time, once you determine the method of fastening, covers will come apart easily. If they get hung up, there may be an undetected screw or snap still in place.

    The most annoying (to be polite) situation is when after removing the 18 screws holding the case together (losing 3 of them entirely and mangling the heads on 2 others), removing three subassemblies, and two other circuit boards, you find that the adjustment you wanted was accessible through a hole in the case just by partially peeling back a rubber hand grip!

    When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken or have their insulation nicked or pierced and that they will not get caught in moving parts. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well.

    Getting built up dust and dirt out of a equipment

    This should be the first step in any inspection and cleaning procedure.

    Do not be tempted to use compressed air!

    I would quicker use a soft brush to carefully dust off the circuit boards and power supply. Work in such a way that the resulting dust does not fall on the mechanical parts.

    For intricate mechanisms, using compressed air could dislodge dirt and dust which may then settle on lubricated parts contaminating them. High pressure air could move oil or grease from where it is to where it should not be. If you are talking about a shop air line, the pressure may be much much too high and there may be contaminants as well.

    A Q-tip (cotton swab) moistened with politically correct alcohol can be used to remove dust and dirt from various surfaces of the deck (in addition to the normal proper cleaning procedures for the guides, rollers, heads, wheels, belts, etc.)

    What to do if a tiny tiny part falls inside

    We have all done this: a tiny washer or spring pops off and disappears from sight inside the guts of the unit. Don't panic. First - unplug it if AC powered. Remove the battery pack if possible from a portable device.

    Try to locate the part with a bright light without moving anything. You may have gotten lucky (yeh, right). Next, over an area where a dropped part will be visible (not a shag carpet!), try any reasonable means to shake it loose - upside down, a little gently tapping and shaking, etc. A hard surface is better in some ways as you might hear the part drop. On the other hand it may bounce into the great beyond.

    If this does not work, you have two options:

    1. Assume that the part has landed in a place that will not cause future problems. There could be electrical problems if it is metallic and shorts out some circuitry or there could be mechanical problems if it jams some part of the mechanism. There is an excellent chance that the part will never cause any harm. What chance? I don't know, maybe 99%. It is not worth taking the unit to pieces to locate the part. You are more likely to damage something else in the process. Obtain a replacement and get on with your life. The exception is, of course, if you now begin experiencing problems you **know** were not there before.

    2. Take the unit to pieces in an attempt to locate the part. For all you know, it may be clear across the room and you will never find it inside. If all the gymnastics have not knocked it loose, then it may be really wedged somewhere and will stay there - forever. If the unit behaves normally, then in all likelihood it will continue to do so.

    To prevent this sort of thing from happening in the future you will no doubt be much more careful. Sure you will! Some suggestions to prevent ejection of an E-clip, split washer, or spring into the great beyond:

    1. Construct a paper dam around the area.

    2. Tie a thread or fine wire around the part before attempting to remove it. Keep this 'safety line' on until after it has been reinstalled, then just pull it free.

    3. Keep one finger on the part as you attempt to pop it free.

    4. Hold onto the part with a pair of needlenose pliers or tweezers while prying with a small screwdriver.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Audio Cassette and Open Reel Tape Equipment

    Parts of an audio tape transport

    The following description applies to most cassette and open reel tape transports including those used in portable and microcassette recorders, Walkmen, and telephone answering machines.

    Looking at the top of the deck such that the tape heads are at the bottom:

    General guide to tape deck cleaning and rubber parts replacement

    The following procedures apply to boom boxes, cassette decks, microcassette and other portable tape recorders, open reel tape decks, and telephone answering machines. While the tape transports used in these devices are less complex than those used in VCRs and other helical scan recording equipment, some routine maintenance can go a long way towards preventing future problems. All the guideposts, wheels, and rubber parts should be inspected and cleaned periodically - how often depends on usage. Of course, no one really does this unless something goes wrong.

    Qtips and alcohol (91% medicinal is ok, pure isopropyl is better. Avoid rubbing alcohol especially if it contains any additives) can be used everywhere EXCEPT on the rotating heads of VCRs and camcorders (and other helical scan devices like 8mm and 4mm (DAT) storage drives) - see the document: Notes on the Troubleshooting and Repair of Video Cassette Recorders for detailed procedures on cleaning of video heads - you can destroy the most expensive part of your VCR by improper cleaning techniques. Dry quickly to avoid leaving residue behind. Sometimes good old fashioned water (just a damp cloth) will work better on sugar based gunk and other kids' grime.

    Cleaning may get your machine going well enough to get by until any replacement rubber parts arrive.

    Things to clean:

    (Some of these components may not be present in your particular equipment).

    A note about alcohol: Some people have suggested that certain alcohol may attack some types of rubber used in these mechanisms. This is certainly true if the rubber is already deteriorated but I have not seen this on rubber that is just dirty, not deteriorated as long as the rubber is not allowed to soak in the stuff! However, Windex (window cleaner) has been suggested as a better alternative.

    Lubrication of electronic equipment

    The short recommendation is: Don't add any oil or grease unless you are positively sure it is needed. Most parts are lubricated at the factory and do not need any further lubrication over their lifetime. Too much lubrication is worse then too little. It is easy to add a drop of oil but difficult and time consuming to restore a tape deck that has taken a swim.

    NEVER, ever, use WD40! WD40 is not a good lubricant despite the claims on the label. Legend has it that the WD stands for Water Displacer - which is one of the functions of WD40 when used to coat tools for rust prevention. WD40 is much too thin to do any good as a general lubricant and will quickly collect dirt and dry up. It is also quite flammable and a pretty good solvent - there is no telling what will be affected by this.

    A light machine oil like electric motor or sewing machine oil should be used for gear or wheel shafts. A plastic safe grease like silicone grease or Molylube is suitable for gears, cams, or mechanical (piano key) type mode selectors. Never use oil or grease on electrical contacts.

    Unless the unit was not properly lubricated at the factory (which is quite possible), don't add any unless your inspection reveals the specific need. Sometimes you will find a dry capstan, motor, lever, or gear shaft. If possible, disassemble and clean out the old lubricant before adding fresh oil or grease.

    Note that in most cases, oil is for plain bearings (not ball or roller) and pivots while grease is used on sliding parts and gear teeth.

    In general, do not lubricate anything unless you know there is a need. Never 'shotgun' a problem by lubricating everything in sight! You might as well literally use a shotgun on the equipment!

    Tape head demagnetizing

    With audio tape decks, demagnetizing is often recommended to improve sound quality and frequency response. There is some debate as to how much benefit there is to this practice but if done properly, there is little risk. Demagnetizing removes the residual magnetic fields that can build up on ferrous pole pieces of the tape heads and various guideposts and other parts in the tape path which may affect frequency response.

    Use a small demagnetizer designed for a tape deck or cassette deck. See the section: Homemade audio tape head demagnetizer if you don't have one or don't want to buy one. However, do not use anything that might be too powerful or a bulk tape eraser which would certainly be too powerful.

    Make sure the tip is covered with a soft material to prevent damage to the finely polished surfaces in the tape transport.

    The tape deck should be off (unpowered) during this process. (Strictly speaking, this doesn't really matter but it's just safer that way.)

    Turn power on to the demagnetizer when a couple of feet away from the unit. Then, slowly bring it in close and slowly go over all surfaces of anything that the tape contacts or comes close to in the tape path. The key word here is **slowly**. Move fast, and you will make the magnetic fields stronger. When finished, slowly draw the demagnetizer away to a distance of a couple of feet before turning it off.

    Homemade audio tape head demagnetizer

    A perfectly serviceable tape head demagnetizer can be easily constructed using a large nail, 100 turns of insulated wire (just guessing here) and an AC wall adapter (from an obsolete modem, for example). Grind down the end of the nail so that it is not sharp and coat it with a soft material or cover the end with electrical tape to protect the finely polished heads from scratches.

    Adjust the number of turns and input voltage for desired strength. How strong should it be? A direct comparison with a commercial unit would be best but when in close proximity to a steel surface, you should be able to feel the 120 Hz attraction but it shouldn't jump out of your hand! Sort of like "Use a pinch of salt you will know how much" :-)

    Building a bulk tape eraser

    A variety of approaches work for this - all based on strong magnetic fields. These will erase floppy diskettes, audio and video tapes, and all your credit cards and Turnpike passes!

    (From: Steven L. Bender (buqu35d@prodigy.com).)

    You need a power transformer about 3" in each direction, can be like a low voltage 12 volt / 3 Amp unit or rated higher. Remove end bells if any, remove all the metal laminations (break the first one, yank it, and the rest will come easier). Re-insert all the metal laminations facing in the same direction, with the "E" all pointed the same, re-glue, varnish, or whatever. Connect AC Plug to the Primary, then insulate the whole works with Plastic tape and outre layer of Duct tape. After insulating it with several layers of tape - Instant Bulk Eraser.

    WARNING: Do not apply power for more than 60 seconds at a time! (It will get hot and burn your hand after two minutes.)

    I had one of those for some years, but accidentally left it plugged in, (pulled the wrong wire out of the 6 to 1 outlet box) and after a few minutes, it smelled and was too hot to touch, and made a nasty noise as the copper started to melt... (Sounds Effects of Liquid Krell Metal in the distance...., Forbidden Planet - Paramount, 1956).

    Luckily I didn't walk out, another few minutes and it would have caught fire..

    I am not liable for any personal, profession, or consequential damages from use of this information !!!

    (From: Steve Walz (rstevew@armory.com).)

    Use a transformer and remove the EI core pieces and replace all the E's only in the same direction. Current limit it with a wire-wound resistor so it doesn't overheat and put a momentary pushbutton on it and a power cord to wall AC and insulate it so you don't shock yourself. Then place it so the open face of the E core pieces faces the tape or disk or whatever to be erased and push the button. Run it all over both sides of the tape or disk and pull the tape or disk away before letting up on the button if you wish to erase it. If you wish to magnetize a tool or such, simply let up on the button while the object or tool is still in contact with it. That's how that works! (You may have to do it a couple times before you catch the AC cycle at the peak! --- Sam.)

    (From: Pat Swayne (me@patswayne.com).)

    Here's a safety tip for your homemade bulk tape eraser: Use a small length of very thin solder as a fusable link. Place this as close to, but insulated from, the primary windings as possible, and pass the current through it. If the thing gets too hot, it will melt the solder and break the connection.

    (From: Sam.)

    It would have to get mighty hot for that to be effective but it's cheap enough. Of course, a thermal fuse or thermostat would be a more well controlled alternative.

    Splicing of audio tapes

    If a tape is broken or seriously crinkled, cutting out the bad section and joining the remaining ends will be necessary. There are special splicing kits for this. I don't know if a place like Radio Shack carries these but an audio dealer or electronics distributor should have one. In a pinch, you could very carefully use a razor blade or Xacto knife to cut the tape an a 45 degree angle and ordinary transparent to mend it. Then, it is best to copy the tape to a new one. At least with an audio deck, you don't really have to worry about ruining the heads with an improperly made splice though you do want to avoid depositing adhesive from the mending tape onto parts of the transport!

    Tape or cassette deck, recorder, or Walkman transport problems

    The following are common problems with audio tape transports:

    1. No movement in PLAY or REC - most likely capstan is not turning or not engaged. If the motor is not working (listen for a hum from inside the transport), refer to the chapter: "Motors and Relays". Otherwise, see the list below.

    2. Tape eating - the capstan is turning but the takeup reel is stationary or not turning rapidly enough to take up the tape as it feeds from the capstan/pinch roller.

    3. FF and/or REW are inoperative or sluggish - assuming the motor is working, the driven reel is not being powered at all or does not have sufficient torque to overcome the tape friction. The driven reel alone must pull the tape through the transport.

    Note that the required torque for the driven reel is much less for PLAY and REC compared to FF and REW as the capstan in contact with the pinch roller pulls the tape from the supply reel.

    The most likely causes are similar for all of these symptoms. The driven reel and/or capstan is not turning due to:

    If the cause is not immediately evident once the bottom of the transport is visible, try to observe exactly what is happening when you play a garbage tape or run the deck with no tape present. Look for broken parts or bits of parts that may have failed off.

    If the transport shuts down shortly after entering any mode, check for a missing or stretched tape counter drive belt or a defective reel rotation sensor. The tape eating protection circuits are shutting down the unit improperly due to a lack of reel sensor pulses. A related symptom will be that the tape counter (mechanical or electronic) does not change during the period when the tape is moving.

    If the logic is not properly controlling the various solenoids or other actuators in a 'soft touch deck', then a service manual will be needed to proceed much further.

    Tape transport azimith adjustment 1 (single REC/PLAY head)

    When prerecorded tapes or tapes recorded on another deck sound muddy, the azimith alignment of the suspect deck may have shifted or be misadjusted. Azimith refers to the angle that the record/playback head gap makes with respect to recorded audio tracks. This angle should be exactly 90 degrees. If it is not, than high frequencies will tend to be reduced in amplitude during playback of a tape not recorded on this machine. Similarly, a tape recorded on a transport with an improper azimith setting will sound muddy on a properly adjusted deck.

    A simple test to determine if azimith alignment is your problem is to record some music on your machine and immediately play it back. If this recording sounds fine but it sounds muddy on another deck, then improper azimith alignment is the likely cause.

    If the recording is still muddy, your deck may have electronic problems like excessive bias (check to make sure you have selected the proper type of tape or bias setting), a worn record/playback head, or the heads or other parts may be magnetized (see the section: Tape head demagnetizing. However, dirty heads as well other mechanical problems can also result in weak muddy sound. See the section: General guide to tape deck cleaning and rubber parts replacement.

    The best way to adjust azimith is while playing a recording that was made on a known good deck - commercial tapes are usually (but not always) a good choice.

    WARNING: once you adjust the azimith, any tapes previously recorded on this transport may sound muddy. If you only record and play your own tapes on this deck, you may want to just leave it alone.

    The azimith adjustment is usually a screw that pivots the record/playback head. It may be spring loaded and possibly fixed in place with a some Loctite or varnish. Often it will be accessible through a hole without removing any covers but not always. Look for it while in play or record mode in back of any holes (which you had no idea had a purpose until now). If there are no access holes, you will have to remove the loading door, cover, or front panel. Be sure you have the correct screw before turning wildly - others may affect critical height or simply be mounting screws.

    Play a tape with lots of good highs - classical instrumental music or jazz are excellent. Now, simply set the azimith adjustment for best sounding and strongest high frequencies which should result in most natural sound. Go slow - a 1/16 of a turn is significant. Turn the screw back and forth and leave it in the best sounding position. Carefully put a dab of Loctite or nail polish on the screw to prevent it from moving.

    Tape transport azimith adjustment 2 (separate REC/PLAY heads)

    This applies to 3 head decks where there are separate record, playback, and erase heads. First, read the section: Tape transport azimith adjustment 1 (single REC/PLAY head). Once you have located the correct adjustment screws:

    1. Using a known good tape (a commercial tape perhaps), adjust your Playback (PB) head azimuth for best high frequency (treble) response.

    2. While recording from a source with lots of high frequency (e.g., a string quartet or composition for brass) and monitoring using the PB head, adjust the REC head azimuth for best treble response. Note: do the adjustments a bit at a time since there will be slight delay until they take effect due to the spacing of the REC and PB heads.

    Walkman/Discman power or sound intermittent

    Note: for actual tape speed, operation, or sound quality issues, start with the section: General guide to tape deck cleaning and rubber parts replacement.

    The socket that the AC adapter or headphones plug into is often quite abused during normal operation. This can lead to broken solder connections where it joins the circuit board inside the unit. Test for this possibility by wiggling the plug without moving or flexing the cable itself. If the sound cuts in and out or the tape player starts and stops or the radio goes on and off, or the CD player resets or stops, then there is likely a bad connection here. Note: eliminate the alternate possibility that the AC adapter or headphone cable is bad by wiggling and tugging on the cable while holding the plug steady. Further verify that it is not simply a matter of dirt or grime interfering with a good connection.

    The connections can be easily resoldered but you will need to open up the case using. Hopefully this will only require jeweler's screwdrivers and great care. (However, some Walkmen are constructed such that access to the interior is virtually impossible without a hand-grenade.) To repair the connections, use a low wattage iron and fine rosin core solder. Make sure you do not introduce any solder bridges. Try not to lose any of the microscrews.

    Cassette or tape playback - one channel dead

    This could be a bad playback head, bad connections, or a bad component in the playback electronics.

    First, confirm that the problem is not in your headphones, patch cables, or the remainder of your audio system - try an alternate audio source where possible.

    To determine if the playback circuitry is working, gain access to the terminals on the playback head - a metal cased little cube near the center of the tape side of the cassette. There should be four wires coming from it. While the machine is supposed to be playing, touch the end of a jeweler's screwdriver gently to each of the four terminals in turn. When you touch the good channel, you should hear a buzz from the appropriate speaker. If you touch one terminal and get a buzz from the 'dead' channel, then it is possible that the head is bad for that channel. If you can touch two different terminals and get a buzz in the bad channel for both, the it is likely that the ground connection to the input preamp has fallen off. If you do not get anything from the bad channel, then there is likely an electronic problem in that channel. Bad connections aside, the most common problem area would be the audio amplifier - bad IC or capacitor.

    Distorted or erratic recording

    First determine if it is a record or playback problem - play a tape recorded on another machine or a commercial prerecorded tape. Try a tape from this machine on another known working tape player.

    If record is the problem and it has very distorted sound, this may be a sign of a bad bias oscillator or switching circuit or record switch. The bias is an ultrasonic signal that is impressed on the tape along with the input signal. Without it, the sound will be highly distorted. In effect, it is a linearizing signal.

    Check that the record select switch is clean - it may have many contacts and may have collected a lot of crud. If behavior changes with each activation of the record switch, get some contact or tuner cleaner spray and use the extension tube to spray inside the switch (with the power off), put the switch through its paces several times and allow to dry before powering it up.

    If it is a portable subject to abuse, check for bad connections as well, especially if, say, one channel comes and goes.

    Beyond this, you can try to measure the signal going to the record heads while in record mode. You should be able to see a high frequency signal in addition to the input signal. If the either of these is absent, then you need to trace back to its source and at this point will probably need a schematic.

    Previous recording not erased

    In this case both the original and new audio appear on the tape. The most likely cause (assuming your deck doesn't have some fancy sound-with-sound or sound-on-sound modes that may be engaged) is a faulty erase head or its driving signal.

    The erase head precedes the record head and probably uses the same high frequency signal as that for record bias to totally wipe the previous recording. (However, on really really cheap tape recorders, erase may just be performed by a permanent magnet.) If the new recordings are really distorted, the bias oscillator itself may not be working. The erase head is either part of the REC/PLAY head assembly or a totally separate head. Check for broken wires to this head as well. If you have an oscilloscope, monitor the signal during record. The erase head could also be defective or really dirty.

    Cassette player erratic autoreverse

    Some of the autoreverse decks use a rotating magnet under or part of the each reel and a reed switch or hall effect device to detect lack of motion and do the autoreverse thing.

    I had one from a Toyota where the plastic drive gear which included the magnet and was part of the reel split and was getting stuck at the broken tooth causing a reverse and eventually eating the tape. It was $9 for that little plastic gear.

    Others are entirely mechanical and if there is a lack of lubrication, dirt, tired belts or idlers, or broken parts they may start acting erratically.

    Although there could be an electronic fault, carefully examine the mechanism for obvious or subtle problems before breaking out the 'scope.

    The following methods are use for autoreverse:

    1. Optical sensor detecting the clear leader on the cassette. Better tape decks use this for sensing at the end so that the reverse occurs just quickly at the end of the tape rather than waiting for the leader to go by and a second or two for the tape to stop.

    2. Totally mechanical where a lever arm presses against the tape and when the tension increases with the reel stopped, it trips a mechanism to reverse.

    3. Optical sensors on reel rotation.

    4. Magnetic sensors on reel rotation - either hall effect devices or simple reed switches.

    If the transport will run without a tape in place, see if the takeup reel is rotating properly and whether the reverse still occurs. If reel rotation is normal but it still reverses, the either you have the optical tape end sensor or there is some fault in the sensors for the reel rotation. If the takeup reel does not rotate, then as suggested above, check for bad belts or idler tire.

    Belts and idler tires are readily available from places like MCM Electronics.

    Autoreverse audio not correct for either or both directions

    This may mean that one or both directions is weak or erratic or that both sets of tracks are playing simultaneously (one in reverse).

    There are three common ways of implementing autoreverse with respect to the tape heads:

    1. Locate both the record/play heads and erase head on an assembly that can rotate (flip) 180 degrees depending on the direction. Mechanical stops determine the precise position.

    2. Locate both the record/play heads and erase head on an assembly that can shift transversely across the tape by one track distance depending on direction. The connections to the L and R channels must be interchanged electronically in this case for one of the directions.

    3. Provide a complete set of heads for both directions. Selection is then done electronically or via a set of switch contacts controlled by the direction reversing mechanism. (This would require duplicating 6 heads for a full record/play deck so it is more likely with a simple player which would then only require a total of 4 heads.)

    Problems may be mechanical or electronic. However, it is probably not what you would consider head alignment.

    In either design, the mechanism could be gummed up and not being properly positioned in one or both directions. There could be broken cables or bad connections since (particularly with (1) and (2).)there could be significant cable movement.

    Check, clean, and lubricate the mechanics first before considering electronic faults. However, since all of these must select channels based on direction, electronic or switching problems are quite possible.

    Walkman plays both sides of tape at once

    One set of tracks will be playing backwards which may make for interesting conversation! There are two possibilities:

    General tape speed problems - slow, fast, or dead

    Are the speed problems sudden or gradual? Over what period of time? Seconds, minutes? For portable devices, are you using a good set of their recommended type of batteries? If the error in speed is significant, then there is something wrong. It isn't a matter of an adjustment!

    Did this problem start suddenly or was this a tape recorder you found buried under an inch thick layer of dust in an attic?

    If the latter, then there could very well be multiple mechanical problems due to deteriorated rubber parts - replace then or toss it.

    Fast play could be an indication of a hard deteriorated pinch roller. Or, you could have forgotten to turn off a 'fast dub' or 'quick copy' switch!

    Clean and lubricate the mechanism. Check for dry or tight bearings.

    Is there any pattern to the problems - like with respect to the start and end of cassettes?

    Where the tape speed has suddenly become excessive, here are some possibilities:

    1. Mechanical. If you had a recent tape eating episode, there may be a wad of tape wrapped around the capstan. Remove it. Alternatively, the pinch roller may not be fully engaging against the capstan and the takeup reel is simply pulling the tape through without any speed control. Clean the mechanism, check for tired belts and springs.

    2. Electrical. The motor speed control is not working. This may be either a mechanical governor inside the motor or a voltage regulator or other electronic control often also inside the motor. In the latter case, you may be able to disassemble the motor and repair it. One possibility is that the series regulator has decided to turn into a short circuit. This may be external or internal to the motor.

    3. Cockpit error. Some tape recorders and tape decks have various features (which you no doubt never use) that may have been inadvertently turned on or twiddled (perhaps by your 3 year old). These include high speed dub as well as selectable and/or adjustable record or playback speed.

    Slight tape speed error may simply mean that an internal adjustment is needed. There may be an access hole on the motor or an external pot. (Use a plastic tool to avoid shorting out something!) However, keep in mind that any tapes you recorded on this machine (assuming it can record) recently will play at an incorrect speed once you adjust the speed.

    Is it slow and steady - no more wow and flutter than normal? Or slow and erratic indicating that (1) the speed regulator is faulty, (2) some bearings may need oil, (3) the pinch roller is glazed.

    If the mechanics seem ok, then check for electronic problems with the motor or regulator. Sometimes there is a trimpot for speed adjustment inside or external to the motor. A faulty regulator or even a bad connection may be the cause.

    A variety of techniques are used to regulate the record/playback speed:

    1. Mechanical governor inside motor - centrifugal contacts open at correct speed reducing current to motor. If speed is too low, than springs could have weakened or contacts could be bad - open. If speed is too high, contacts may be welded closed. There may be a resistor and/or capacitor across the contacts. An open resistor could conceivably cause unstable speed fluctuations. A capacitor may be present to reduce electrical noise.

    2. Voltage regulator inside motor case or external to motor. The regulator or transistor may be faulty. If power for the motor seems to come directly from an unregulated supply, check across the motor terminals with an ohmmeter. A low reading which is identical in both directions would indicate a direct connection to the motor brushes with no internal regulator (or perhaps a shorted regulator). A high reading or one that is different in each direction indicates an internal electronic regulator - or you could just use your eyeballs to determine if there are any electronics inside the motor. These can be disassembled and bad parts replaced. There may be an access hole on the motor for an adjustment. (Use a plastic screwdriver for the adjustment to avoid the possibility of shorting something inside the motor!) Alternatively, you could remove the guts and install an external regulator using an LM317 or similar part.

    3. Active regulator with tachometer feedback from motor winding - there would be 4 wires instead of two coming out of the motor - 2 for power and 2 for tach. Control circuitry could be bad or the tach output could be dead (speed too high).

    4. If an optical strobe disk is located on the motor shaft, then it may be part of a speed control circuit. If it is on one of the reels - probably the takeup reel - then it simply operates the (electronic) tape counter or signals the controller that the takeup reel is turning - to catch tape spills.

    For flutter problems specifically:

    (From: Nicholas O. Lindan (nolindan@ix.netcom.com).)

    1. Dirt on the capstan. Clean encrustations with fingernail. Remove remaining dirt with chamois or q-tip dipped in windex.

    2. Worn or dirty pinch roller. Clean with Windex -- some alcohols can attack some pinch rollers making them sticky. Replace if worn, 'dented', hard or really sticky.

    3. Especially on Walkman: lack of lubricant on pinch roller bearings. Pick up a tiny droplet of 'Nye Clock Oil', sewing machine oil, or ATF (automatic transmission fluid) and apply top and bottom to ends of the shaft/bearing.

    Tape speed problems on older equipment

    Older reel-to-reel decks (maybe even some cassette decks) likely use an AC induction or synchronous motor driven from the power line. Speed selection is usually done by switching in different sets of motor windings and the use of slip-on capstan/pinch roller sleeves.

    Speed problems are most likely a result of

    See the appropriate sections in the chapters: "Turntables" and "Motors and Relays" for specific information on these types of problems.

    Tape speed adjustment made easy

    OK, you have found the magic screw, but how to set the speed accurately? Sometimes, there will be strobe disks on tape decks which will appear stationary under fluorescent lighting (magnetic ballasts only - electronic ballasts are usually high frequency and do not modulate the light intensity at the power line frequency) but not usually. So, you do it by ear:

    Make a recording of a single tone on a tape recorder you trust - one with accurate speed.

    Suitable sources include: a signal generator, electronic instrument, Touch-Tone phone tone, PC sound card output or PC speaker, etc. A frequency around 400-1000 Hz should work well.

    Then, adjust the speed while listening to this same source simultaneously with the tape being played back on the unit to be adjusted. As you adjust the speed, you will hear the pitch change. As it approaches the correct setting, you will hear the tones beat against each other. When you are set correctly, the pitches will be equal and the beat frequency will go to zero. Even if you are tone deaf, you will easily be able to adjust pitch accuracy to better than 1/10 of a semitone using this method.

    Recording the 60 or 50 Hz power line (through a suitable isolated attenuator) and using this as a test tone will work if you have an oscilloscope. Trigger on 'line' and adjust playback speed to stop the trace from drifting. However, this is too low a frequency to be used accurately with your Mark I ears!

    Some alternatives:

    (From: Helling Bernie (helling@uwindsor.ca).)

    A while ago I hit upon a way to set the speed on old cassette decks that have gone out of speed.

    Use an electronic guitar tuner

    They cost about $40, can be borrowed, etc... Find a pro cassette deck that is in speed, (the local campus radio station had a nice one) and record a tape full of A tone. My guitar tuner puts out tones too, so that was easy....

    Play the tape in the suspect deck, while adjusting the motor trim to replay a A tone perfectly on the tuner meter...

    Tadah....

    I never did have the patience to learn to play the guitar, so I got some use off the tuning meter....

    (From: Paul Temple" (mri@earthlink.net).)

    Get a song on CD and a tape of the same album. Play both at the same time and adjust away!

    Sudden increase in flutter on tape decks or Walkmen

    If your prized Walkman suddenly develops a severe case of warbling sound check:

    1. Batteries (where appropriate). Almost dead batteries will greatly increase flutter. Use of Nickel-Cadmium rechargeable batteries in place of alkalines may result in problems due to their lower voltage (1.2 V vs, 1.5 V per cell).

    2. Tired belts - loose flabby deteriorated belts will produce varying, probably slow, speed as well.

    3. Dirt or goo on pulleys. Sometimes a glob of stuff gets stuck to a pulley and produces a periodic variation in speed. I picked one up at a garage sale that had this problem. I thought it was a bad motor until a careful examination revealed that the belt was jumping a mm or so on each rotation of an idler pulley.

    4. Lack of lubrication - a dry or worn bearing may result in a variety of speed problems.

    5. Bad speed regulator - either mechanical or electronic including bad solder connections or cracks in circuit board traces.

    6. Bad power supply.

    7. Bad tape. Don't overlook this obvious possibility, try another one.

    Annoying tick every 30 seconds or so from audio output

    This may be an almost inaudible tick, click, or pop which occurs fairly regularly. Its frequency may be dependent on many factors including temperature, humidity, even whether you are at the start or end of a cassette! I may occur even if no cassette is present but the motors are running.

    The tick is probably due to a static discharge though other causes are possible including mechanical problems and bad capacitors in the power supply.

    (From: Paul Grohe (grohe@galaxy.nsc.com).)

    The problem is with a plastic or nylon gear, in contact with a rubber belt or tire, generating a charge and discharging to some nearby metal. (It acts just like a miniature Van De Graff generator --- sam.)

    You have to listen around for it. Murphy sez it will probably be buried deep in the "guts" of the machine ;^)

    I found it by touching a small wire to each of the pulleys until it stopped "snapping" (actually, I got a little "snap" when I found it).

    My "cure" was to use some stranded wire to create a "brush" that lightly brushed against the pulley to bleed off the charge to the chassis.

    I would first check the two big capstan flywheels and anything powered by the main motor belt. Look for any plastic, or metal with plastic bushings and parts in contact with belts or tires.

    (From: Ylo Mets (ylo@mango.mef.ki.se).)

    I have experienced similar ticking in an old two-motor deck. There was some dust collected between the takeup/wind motor shaft end and the metal chassis, which evidently generated static electricity. Cleaning the dust did the trick, although at first I thought the shaft was too close to the metal chassis. You can check for the static by breathing slowly into the mechanism. The damp air should discharge the static and the frequency of ticks decreases. Such ticking is especially annoying because it is not exactly regular.

    Reel-to-reel tape deck problems

    "I have a Teac 2300S reel to reel. 7" reel capacity, 1/4" tape. Two problems. First, right channel doesn't play back. Second, pinch roller doesn't come up to the capstan unless it's gently pushed."

    (From: Davetech (dnesbitt@mindspring.com).)

    I've repaired a few reel-to-reels in the past and generally find that they all need three main things done:

    The last one I did, the old grease had hardened up so much that the heads would not come up to contact the tape - and the grease was so hardened that I could not get the linkage pulled off even using pliers and pulling as hard as I could. I had to heat the post with a propane torch before the old grease would soften enough that I could separate the parts.

    I put enough time in the last unit that I could have fixed 3 or 4 VCR's, so I'm not real big on taking them in. They are generally very time consuming to disassemble and reassemble and overhaul. But not usually technically difficult to fix.

    Tape creeps off capstan

    "I have a Sony reel-to-reel tape recorder. When I play a tape, after a few seconds or minutes of playback, I can watch the tape creeping up the capstan between the rubber roller until it comes out the top and off the capstan."

    The first thing to check - as with a VCR with similar symptoms - is the condition of the rubber parts, in particular, the pinch roller. Next, would be tape path alignment and wear:

    (From: Jack Schidt (dbutler@airmail.net).)

    Check the reel height as well. Capstans are upset if the reel tables have shifted. Use a straight edge between the two reel tables. There are set screws that sometimes get loose on some of these machines.

    Check for a worn capstan bushing. Disconnect the drive belt (if any) and see it there is lateral play in the capstan. If so, perhaps you can shim it (either the motor [if equipped] or the idler).

    Also make sure the tension is simply not too high. You should be unable to pull the tape through, but ridiculous force (as in something is BENT) will cause this problem as well.

    8-track player problems

    These compete with turntables for classification in the Jurassic era. 8-track equipment uses a cartridge with a single reel and enless loop tape (tape is pulled from the center and returned to the outside). The tape can only move in the forward direction - rewind is not possible.

    There were also similar competing but incompatible 4-track systems as well as quadraphonic 8-track (when quad was all the rage).

    Four pairs of channels allow for many hours of stereo playback without changing cartridges. A pair of playback heads is mechanically shifted among the 4 possible sets of tracks when a metallic strip on the tape passes over a set of contacts which operate a solenoid.

    Most common problems are - you guessed it - mechanical with the cartridge or in the drive or head shifting mechanism. General comments with respect to cassette decks apply here as well.

    If you are really interested in resurrecting that 8-track player found under the steamer trunk in your aunt's attic, there are many links to information on 8-track equipment, books, history, dealers, collecting, and everything else 8-track related that most people probably don't care much about anymore at the following web site:

    There may be links for specific 8-track player repair information but I could not locate them at this site.

    However, this one seems to be the place to go for step-by-step 8-track cartridge repair:

    Repairing a cassette tape

    (From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org).)

    This will be either easy or very hard. Question: do both of these have SCREWS holding the tape together? If yes, EASY, if not, very HARD!

    See what I'm getting at? Go to the store and get a quality tape that ALSO has screws holding it together... you will transplant the insides into the new cases. Take off the screws from both (old and new tape, do it one tape at a time). Remove both top covers - make sure you don't lose the thin plastic "lubricant" sheet (if any). Swap the tape reels - BE VERY SURE the old one doesn't go flying off or it's more or less toast. Put the old tape reels into the new case, make sure the tape follows the same path as the one you took out did - so it doesn't get trapped by the case when you replace the top. Put the "lubricant" sheet back on top of the two reels of old tape and replace the top. Put in all 5 screws. There you go. I'd say that this is 100% successful every time I've tried it.

    If your tapes don't use screws but are, rather, glued together, you're on your own. I suggest a VERY sharp utility knife but tape damage is, alas, a very REAL possibility.

    Another way you can do this if you want to also replace the REELs (or if it's a sealed unit) is to rewind the old tape, cut the tape LEADER and attach it to the new cassette that you have already gutted. Put the new tape together (2 screws will do) and attach a small motor to the takeup reel. When the tape has been transfereed to the new reel, cut it off the old one (the old cassette is now empty) and open the new one again, attach the tape to the reel and put it back together using all screws. Other than the leader being 2" shorter, you have the old SOUL in a new BODY.

    Of course, watch out that you wind the tape EXACTLY as it was and not on the other side... etc. etc. I have done this twice. Grrrr.

    It's a pain in the rear... so do it only if you have to... I wouldn't do this for money..... if that tells you anything.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Turntables

    Turntable (record changer) maintenance

    Here are general comments on oiling dinosaurs, oops sorry, turntables.

    Usually there is a 'C-clip' or 'E-clip' which holds the platter (the thing that rotates) onto the spindle. It may be covered with a decorative piece which can be easily removed. The clip can be pryed off (gently) with a small screwdriver (just don't lose it, though even this is not a biggie so long as you never turn the thing up-side-down).

    The platter can then be lifted straight up and off the spindle. You will see several things (this will vary depending on your particular unit):

    1. A flat washer, sitting on a ball bearing race sitting on another flat washer (one or both of these washers may be missing. Also, the top one may stick to the platter when it is removed.) The ball bearings, shaft, washers, etc. should all be cleaned with degreaser and then lubed with a light grease. If either the steel balls or the flat washers are corroded, replacement will be necessary or else there will be terrible audible rumble. For now, it will at least work well enough to determine what else, if anything, needs attention. Also clean and lubricate the platter bushing (center hole) and shaft (vertical post on which it rotates).

    2. Changer gears etc. These will have varying amounts of grease on them if it is not gummed up, leave them alone. Put a drop or two of light oil on the shafts. Inspect other linkages as well. If the grease is gummed up on the gears or sliding linkages, you will need to clean it off thoroughly with degreaser and then use a small amount of high quality grease suitable for delicate mechanisms. One cause of a changer failing to activate at the end of a record is gummed up grease.

      However, DO NOT lubricate the sliding parts that actually initiate the change cycle. Just clean them thoroughly. They should rattle when shaken. Not only will grease impede free movement, but it will also attract dust and dirt and get gummed up again very quickly. (This from someone who has been repairing all types of turntables professionally for more years than I can imagine.)

    3. Motor. Check to see if the motor shaft turns freely and smoothly even if spun quickly between your fingers. If it does - without squealing, don't do anything else. If it is tight or makes noise, then you will need to carefully disassemble the motor and clean and lubricate the bearings at each end with light oil. Don't lose any of the various washers/spacers that may be present on the shaft as it is removed from the end pieces and make sure to lubricate and return them to exactly the location and the same order they were in originally.

    4. Clean the rubber parts with isopropyl alcohol and Q-tips or a lint free cloth until no more black stuff comes off and then dry thoroughly. Now, inspect the belts (if any). If belts are flabby or cracked or if they don't instantly return to their relaxed length if stretched 25% and released, they will need replacing. Check the idler tire (if present). If hard or cracked, it will need replacing as well.

    Note: Light oil here means electric motor oil or even 3-In-One but NOT WD40. Light grease means something that is suitable for fine mechanisms and is safe for plastics. Automotive bearing grease may not qualify.

    Where the drive belt is found to be bad, an exact replacement is best. Though something close will work, there may be a very slight change in speed which may or may not bother you (probably not if you either don't have perfect pitch or aren't playing an instrument along with the records). For turntables with servo lock circuitry or a drive motor with a speed adjustment, correction may be possible.

    Speed control in turntables

    Most inexpensive turntables/changers will use a synchronous motor or even just an induction motor. The only maintenance for the motor is cleaning and lubrication. A deteriorated drive belt can result in reduced, probably erratic speed or inability to start altogether.

    Servo controlled turntables utilize a feedback technique which locks the platter speed to a stable reference - either the power line (50/60 Hz) or more commonly a crystal oscillator. Here is one example:

    A Sony turntable I repaired used a magnetic stripe pattern on the inside of the platter which was sensed by a magnetic pickup. The resulting signal was phase locked to a stable reference and used to control a brushless DC direct drive motor. Speed would become erratic if (1) the magnetic pattern were damaged, (2) the pickup position was moved too far from the surface of the platter, (3) the Hall-effect sensors in the motor were bad, or (4) the control electronics went bad. In one case, it turned out that one of the Hall effect sensors had failed in the motor. This required disassembling the motor and replacing the sensor - $4 from Sony.

    To determine whether the turntable is running at the proper speed or for adjusting it, many turntables came with a "strobe disk" built in that used the 60 Hz (or 50 Hz) power line frequency as a reference driving a neon indicator lamp. When the appropriate set of lines on the disc appear stationary under the neon illumination, the speed is correct. In the good old days, such a disc could be purchased at any record store. :) In the modern age, go to Free Speed Check and download one.

    Turntable runs slow or fast after being moved

    This is likely to be a mechanical problem - a belt that has worked loose and is riding on the rim of the motor pulley or the wrong surface of the platter.

    For an AC line driven motor (no electronics between the AC line and motor except possible for a power transformer), it is virtually impossible for any fault to result in a motor running faster than normal. A motor may run slow due to dirt, lubrication, or bearing problems.

    Of course, check to see that any speed selector has not been accidentally moved to the '16' or '78' position!

    For a servo-locked turntable, a misalignment of the sensor used for speed feedback could result in an incorrect - probably higher than normal (and uncontrolled) speed.

    Servo locked turntables

    The basic direct drive turntable consists of a DC brushless motor, some type of platter speed/position feedback, and an electronic control loop - a phase locked loop to regulate speed. Otherwise similar units may use a rubber belt to couple the motor to the platter.

    A variety of faults can occur with these units resulting in incorrect or erratic speed, excessive wow and flutter, or no rotation at all:

    Wow, flutter, and rumble in a turntable

    Wow and flutter refer to undesirable periodic variations in pitch caused by changes in turntable (or tape deck) speed. Wow would be a slow variation (e.g., once per rotation) while flutter would be rapid (e.g., a motor pulley with a bump). Even if very slight, these faults will be all too obvious with music but may go undetected at much higher levels for voice recordings.

    Rumble is a very low frequency noise added to the audio caused by vibration due to cheap, worn, dirty, or dry spindle bearings or by vibrations coupled in from some other motor driven component or even from loudspeakers if the volume is turned way up. If really bad, rumble may sound like a freight train in the next room. Also see the section: Comments on turntable rumble.

    Note that rumble should not be confused with hum - 50 or 60 Hz pickup from the power line. Hum can be virtually eliminated by the use of decent shielded cables (not that expensive, just decent), and making sure that the turntable frame is jumpered to the ground terminal of the amp or receiver. Hum can also result from mechanical causes - the vibration of an inexpensive motor or improperly mounted power transformer in the turntable (or almost anywhere else in the HiFi system). It may not be possible to eliminate some of these sources of hum except by redesign or other major modifications to the equipment.

    For anyone only used to listening to CDs, even very small amounts of and of these will prove very obvious and extremely objectionable. Wow, flutter, and rumble are undetectable - for all intents and purposes nonexistent - with even the cheapest junkiest CD player.

    For a common motor driven turntable, the following are likely causes:

    1. Bad belt or idler. Rubber 'rusts'. If it is old, then almost certainly the rubber parts have deteriorated and will need replacement. Unfortunately, replacement parts are not as readily available as they once were. The places listed at the end of this document may have some and there are many other sources but it is not as easy as one would like.

    2. Dirty or worn spindle bearing. This will cause rumble. The thrust ball bearing can be cleaned and lubricated or replaced. The platter bushing can be cleaned and lubricated.

    3. Lump of crud stuck to motor pulley or idler, usually of unknown origin.

    4. Dried up lubrication in motor, idler, or other rotating part. These can be cleaned and lubricated.

    5. Bad motor (not that likely) except for lubrication in which case the motor can be disassembled, cleaned, and lubed.

    6. Physical damage to platter - something heavy was dropped on it upsetting the delicate balance.

    If you are attempting to restore a 20 year old turntable from Aunt Annie's attic, don't even bother to power it up before replacing all the rubber parts and cleaning and lubricating the motor, idler, and spindle bearing.

    Comments on turntable rumble

    Rumble is a low frequency, almost sub-sonic sound that is inevitable with most turntables. A turntable that doesn't rumble is possible but expect to pay about as much as for a small car. Buzz words like 'magnetic suspension and 'dynamically stabilized' drive will probably accompany the stratospheric price tag. :)

    (From: JURB6005 (jurb6005@aol.comtere).)

    A turntable that doesn't rumble may be purchased for a few thousand bucks, but for the rest of us.....

    You failed to mention the type of drive, belt rim (idler) and I doubt it's direct. A rim drive, while it's off should be silent when you whip that platter up to about 200 rpm with your hand. A light platter should keep spinning for at least 2 minutes. The old 12 pound platter should spin for about 5 to 8 minutes. When you first spin it up, listen, in a quiet room to the turntable. You should hear NOTHING. If you hear anything, check those platter bearings and/ or any automatic linkage it may have.

    Note: If it's a belt drive REMOVE THE BELT FIRST!! If it's a rim drive make sure the motor spindle is unscrupulously clean and the idler isn't hardened or out of round. If the rumble only occurs when you turn it loud (like feedback) you need to isolate the turntable from the speakers. This type of feedback rumble can sometimes be reduced by reversing the phase of ALL the speakers. i.e. they are still in phase with each other, but now reversed with respect to the input.

    (From: Philip Nasadowski (nasadowsk@mail.hartford.edu).)

    Also realize - these things aren't silent!!! Try seeing if your amp has a rumble filter (that's what it's there for!) Make sure the motor is clean, the drive wheel is good, etc. Oh yeah, and experiment with various greases on the bearings too. And make sure the order of the washer / bearing washer/ is right.

    I have had the pleasure of enjoying several excellent turntables, the ones that you can put right on top of the speakers and track almost as well as a Zero One Hundred. They've included a Dual 1229, a couple of Elac Miracords and even a transcription grade BSR 810. My favorite was the 1229. And yes, with an Audio Technica AT13 ea (10-30,000Hz) >cartridge, they can sound better than a CD. Good luck.

    Ever try a Grado cartridge? They're nice...

    (From: Jerry Greenberg (jerryg50@hotmail.com).)

    If I can remember correctly, is this the old direct drive turntable with a rubber wheel between the motor shaft and the platter?

    If it is, putting on a new fresh rubber drive wheel will help it out a bit. But, because of the design of this table, there will always be some mechanical hum pickup. It starts at the motor...

    Erratic sound from turntable

    Sound that varies randomly in intensity or where one channel drops out will usually be due to bad connections in the various units. This could be:

    1. At the pickup itself. There may be small press fit connectors at the cartridge. These sometimes become loose. Gently remove each one (one at a time! so that you do not mix up the wiring) and squeeze with a pair of tweezers or needlenose pliers. Snap in cartridges may have dirty contacts the springiness may have disappeared.

    2. At the RCA plugs under the turntable which connect to the tonearm. Depending on your design and problem, you may need to simply clean with contact cleaner or squeeze the metal shell or center contact.

    3. At the receiver, preamp, or amplifier. Same as (2) above.

    4. Sometimes the cables themselves will develop broken wires at one end or the other. Easiest is to try a different set of cables.

    Turntable tracking and skating force adjustment

    Tracking force keeps the stylus in the record's groove. Too little is as bad as too much. It is best to follow the recommendations of the cartridge/stylus manufacturer. If you do not have this information, start low and increase until you eliminate skipping or excessive distortion, buzzing, or stuttering. If too low, the stylus will make only partial contact with the groove during high amplitude segments - it will jump from peak to peak (or other portion) of the wave rather than smoothly and continuously following it. If too high, it will gouge the vinyl (or the shellac or whatever depending on the vintage of your records) or in extreme cases, bottom out on the cartridge's suspension.

    Skating force compensation is applied to compensate for the fact that except at one distance from the spindle (or with a linear drive tone arm where this does not apply), the tone arm is not tangential to the groove. Imagine a perfectly flat record without any grooves. If you 'play' this, the tone arm will be stable at only one position somewhere in the middle - where a line drawn through its pivot point and the stylus is just tangential to a circle at that distance from the spindle. The skating is usually a simple spring which attempts to compensate for this in such a way that the side force tending to move the stylus is minimized at all positions. Otherwise, the inner and outer walls of the groove will experience a different force which will add distortion and affect stereo separate and balance.

    Skating force compensation is usually set based on the tracking force.

    Note that if you are used to CDs or high quality cassettes, all the horrors of records will be all to obvious unless you are using high-end equipment (the kind that likely costs as much as your automobile) and meticulously maintain your vinyl record collection. Sonic defects like wow, flutter, rumble, distortion, noise, imperfect stereo separation, skipping, and limited frequency response are all facts of life for this technology which has not changed in any fundamental way since Edison's time.

    Turntable tracking/skating problems

    (From: Bill Turner (wrt@eskimo.com).)

    You're bringing back memories. I used to work for the leading Magnavox warranty repair station in Los Angeles and I've repaired hundreds of the good 'ol Micromatics.

    Assuming there isn't something actually *pulling* the arm across the record (in other words it's just sort of sliding across on it's own) the problem is almost always the needle. Either the tip is worn out, broken, missing, etc or it could have just been dislodged from it's holder. Lift up the arm and look carefully at the needle. The actual diamond tip is on the end of a short shaft which in turn rests in a fork-shaped rubber holder. This shaft is easily knocked out of the holder, and if that's the case, just carefully put it back.

    Hope this helps. The Micromatic was a fine record player in it's time. Good luck, and let me know if I can help some other way.

    About stylus wear

    So you still have one of those modified potters' wheels on which you place a pre-formed piece of plastic that looks like a flattened dinner plate with a hole in the middle and drag a needle over its surface to produce sound. How can you tell when the needle, err, stylus, has worn to the point (no pun...) of requiring replacement?

    It used to be that you could take it to any record store. They would look at the stylus under a microscope, and after a few choice utterances of "Oh my!" followed by "This will strip the music right off your LPs", and would then tell you that your stylus required replacement IMMEDIATELY whether it did or not :-). Of course, record stores don't exist anymore.

    If you have a semi-decent microscope, you can do the same and get an honest answer ;-). 100X should be more than sufficient, though getting the stylus into position to view it may prove to be challenge.

    The tip of a good stylus looks smooth and is spherical or ellipsoidal in shape. A worn stylus will exhibit edges/corners due to the wear of the tip. Yes, even diamond will wear down if you drag it over thousands of miles of vinyl. Some of your LP record jackets may even have typical photos of good and worn styli so check these out as well.

    If the stylus is visibly worn:

    1. The physical result will be that it will grind away at the grooves in your records.

    2. The audible result of a bad needle will be excessive distortion and loss of high frequencies from (1).

    After you replace it, your old records will still never sound as good as they did before because of (1) :-(.

    Changer won't cycle automatically

    If it is a basic old fully mechanical record changer, this is usually due to gummed up grease. There is a large gear which gets activated to operate the lift-and-place mechanism. Attached to this gear is a small swinging segment that gets jogged by the tone arm reaching the proper position. The grease gets gummy and prevents this. You have to remove the platter.

    If it is a fancier changer with fully electronic controls, then it may be a sensor or something in the circuitry.

    Of course, there was this one I recently worked on where some previous repair person (I am using this term generously) had glued the moving parts of the changer mechanism together so it could not possibly ever have worked again (until I unglued them all).



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Loudspeakers

    Loudspeaker anatomy

    In this document, we use the terms 'loudspeaker' or 'speaker system' to denote a unit consisting of one or more drivers in an acoustic enclosure perhaps along with a frequency selective crossover, tone controls and switches, fuses or circuit breakers. Connections to the amplifier or receiver are via terminals on the rear. The front is covered with an (optically) opaque or semitransparent grille which provides protection and improves the appearance (depending on your point of view).

    A 'driver' is the actual unit that converts electrical energy into sound energy. Most drivers use voice coil technology: a very low mass coil wound on a light rigid tube is suspended within a powerful magnetic field and attached to a paper, plastic, or composite cone. The audio signal causes the coil to move back and forth and this motion causes the cone to move which causes the air to move which we perceive as sound.

    The typical driver consists of several parts:

    Inexpensive 'LoFi' devices like portable and clock radios, many TVs, intercoms, and so forth use a single, cheap driver. Some have a coaxial pair of cones but this does little to improve the frequency response.

    HiFi speakers systems will divide the audio frequency spectrum into several bands and use drivers optimized for each. The reason is that it is not possible to design a single driver that has a uniform response for the entire audio frequency spectrum. A 'woofer' is large and massive and handles the low base notes. A 'tweeter' has a very low mass structure and is used for the high frequencies. A 'mid-range' handles the mid frequencies. There may also be 'sub-woofers' for the very very low notes that we feel more than hear. Some systems may include 'super-tweeters' for the very highest frequencies (which few people can hear. This may make for some impressive specifications but perhaps little else.)

    A 'crossover' network - a set of inductors and capacitors - implements a set of filters to direct the electrical signal (mostly) to the proper drivers.

    Various controls or switches may be provided to allow for the adjustment of low, mid, and high frequency response to match the room acoustics more faithfully or to taste. Fuses or circuit breakers may be included to protect the speaker system from intentional (high volume levels) or accidental (amplifier output stage blows) abuse.

    Loudspeaker problems

    If you have a high quality and expensive set of loudspeaker, then the cost of professional repair may be justified. However, if the problem is with speaker systems you might not write home about, then read on.

    Playing your music system at very high volume levels, especially CDs which may have peaks that way exceed the ratings of your loudspeakers is asking for trouble - but you knew that! CDs can be deceiving because the noise floor is so low that you are tempted to turn up the volume. A peak comes along and your speaker cones are clear across the county (remember the movie 'Back to the Future'?). Loudspeaker systems are generally pretty robust but continuous abuse can take its toll.

    Problems with loudspeakers:

    1. An entire speaker system is dead.

      Verify that the connections both at the speaker system and at the source are secure. Check circuit breakers or fuses in the speaker system. Reset or replace as needed.

      Make sure it is not the amplifier or other source that is defective by swapping channels if that is possible. Alternatively, test for output using a speaker from another system or even a set of headphones (but keep the volume turned way down). Assuming that these tests confirm that the speaker system is indeed not responding, you will need to get inside.

      It would take quite a blast of power to kill an entire speaker system. Therefore, it is likely that there is a simple bad connection inside, perhaps right at the terminal block. You should be able to easily trace the circuitry - this is not a missile guidance system after all - to locate the bad connection. If nothing is found, then proceed to test the individual drivers as outlined below.

    2. One or more drivers (the name for the individual speakers in a loudspeaker enclosure) is dead - no sound at all even when you place you ear right up to it. The cause may be a bad driver, a bad component or bad connection in the crossover network. Test these components as outlined below.

    3. One or more drivers produces distorted or weak sound. Distorted may mean fuzzy, buzzing, or scratchy a various volume levels. Most likely this is due to a bad driver but it could also be a defective component in the crossover - a capacitor for example or even a marginal connection.

    Getting inside a speaker system usually means removing the decorative grille if it snaps off or unscrewing the backpanel and/or terminal block. Use your judgement. With the grille removed, you will be able to unscrew the individual drivers one at a time. With the back off, you will have access to all the internal components. If sealing putty is used, don't lose it or expect to obtain some replacement putty (non-hardening window caulking like Mortite is suitable).

    Test the components in the crossover network with a multimeter. These are simple parts like capacitors, inductors, and potentiometers or reostats. Confirm that any circuit breakers or fuse holders have continuity.

    Test the drivers on the low ohms scale of your multimeter. Disconnect one wire so that the crossover components will not influence the reading. Woofers and midrange drivers should measure a few ohms. If their impedance is marked, the reading you get will probably be somewhat lower but not 0. If possible compare your readings with the same driver in the good speaker system (if this is a stereo setup). Some tweeters (very small high frequency drivers) may have a series capacitor built in which will result in an infinite ohms measurement. Other than these, a high reading indicates an open voice coil which means a bad driver. In a comparison with an identical unit, a very low reading would mean a partially or totally shorted voice coil, again meaning a bad driver. Except for expensive systems with removable voice coil assemblies, either of these usually mean that a replacement will be required for the entire driver. Sometimes an open voice coil can be repaired if the break can be found.

    To confirm these tests, use an audio source to power just the suspect driver. Your stereo system, a small amplifier attached to an audio source, or even a pocket radio (use its speaker output if the headphone output does not have enough power) will suffice. The resulting sound will not be of high quality because you do not have the enclosure sealed and it is only one of the drivers in the system, but it should give you some idea of its condition. Again, comparing with an identical unit would be another confirmation.

    Electrical causes for loudspeaker damage

    These are not going to be covered by any warranty! Of course, not mentioned below are: fire, flood, falling from a tenth story window, getting run over by a bulldozer, or being plugged into the wall outlet instead of the stereo, etc. :-).

    (Portions from: Lasse Langwadt Christensen (fuz@control.auc.dk).)

    1. DC bias across speaker will cause the voice coil to overheat. Windings may short out or open up. Also see (3), below. This usually results from an amplifier output stage failure - shorted capacitor, for example.

    2. High power clipped signal:

      • A clipped signal contains a lot of high frequency energy and that could burn a tweeter, because the voice coil overheats.

      • The clipped signal could have a amplitude so large that the voice coil hits the magnet and is bent. It's a permanent damage but not always terminal, because the might still work, but make a scraping noise. If you play loud with it for a long time (and it doesn't burn out - see (3), the part scraping against the magnet might wear off.

    3. If the speaker is overheated, because of high power for a long period of time, the voice coil could expand and scrape against the magnet, and perhaps short some of the turns. This is not always permanent, and some manufacturers use Teflon on the magnet, so that it's less likely to cause damage.

    Repairing loudspeaker drivers

    As noted above, if you are dealing with a high quality system, leave these repairs to professionals or obtain an entire replacement as some reduction in audio quality may result from the abuse you are about to inflict on the poor defenseless driver.

    We will address two types of repairs: physical damage to a speaker driver cone and an open voice coil (actually, wiring outside the voice coil). However, serious damage to the cone or just plain deterioration of the suspension components may require replacement of the entire driver unless a close enough match can be found.

    For more information on loudspeaker repair, see: "Speakers (big, small, in between)" also at this site.

    (From: Roy J. Tellason (rtellason@pa.net).)

    I've worked with a lot of both Musical Instrument stuff (guitar amps and such) and also pro sound gear (a whole 'nother world, really) and this stuff gets used pretty hard. It's not uncommon to find a driver failure, either from the high levels at which this stuff is commonly used, or the abuse it takes getting hauled around on the road, etc.

    I noted with interest the comments in one section regarding the voice coil rubbing. In the type of thing I'm talking about above, any such rubbing means a bad driver, no ifs ands or buts about it. The test for it is easy -- just push on the cone, from the front side. In some enclosures you may have to remove the driver for this. If there's a problem, you'll hear a rubbing sound, and the driver is a candidate for replacement or re-coning. It should move freely, in both directions, with no rubbing at all. But you need to press evenly with both hands on either side of the middle!

    I also ran across one that had me going for a bit. I'd play audio through it (my stereo supplied the test signal, but through a little box with a pot in it to avoid overdriving the amp), and it sounded okay to me, but the musician who owned it (a piano and organ player) wasn't happy with the way it sounded for him. Piano is some of the most demanding music, with the high transients...

    Anyway, he told me that the unit had been "funny" for him ever since one occasion when the amp had fallen on its face.

    I pulled the speaker out, and was I surprised when I tried the "push test" - that cone didn't seem to want to move _at all_. It apparently moved enough to play the audio I was feeding through it, but not near enough for his use. Not the first time me being a tech but not a musician has given me a bit of trouble...

    One other comment that I can offer is that both MI and Pro Audio folks do a *lot* of re-coning, the prices on a lot of their hardware make it more practical than in most home equipment. These guys can also supply replacement drivers in some pretty hefty configurations, both size-wise and in terms of power-handling capability. I wouldn't recommend putting an MI-type (guitar amp, say) speaker into a pro audio application, though I don't see why the other way around wouldn't work, even if it would be a bit more expensive.

    Repairing speaker driver cones

    Minor damage to the cone can be repaired using a flexible adhesive like weatherstrip cement and a piece of thick paper to reinforce the seam or hole if necessary. Since this will not totally perfect match with the original paper cone, there could be audible distortion at certain frequencies particularly at higher volume levels. However, such a repair will be better than nothing. Cut the paper in a shape and size to just overlap both sides of the torn area or completely cover the puncture. Use just the smallest amount of adhesive to fasten your 'splint' to the cone. The less material you add, the more likely that the audio effects will be minimal.

    Note: Almost any general purpose adhesive can be used. However, it is advised to avoid RTV silicone (bathtub caulk, etc.) since wherever this stuff goes, nothing else will every stick again. For a little hole, this probably doesn't matter but you definitely don't want to replace the surround with it!

    (From: M. Przytarski (m.r.p.@ix.netcom.com).)

    I have repaired many field-coil speakers, and there is one sure proof way my grandfather showed me (and several Tube Radio rebuilding mags suggest the same).

    Take a milk glue (Elmers or such), and rub it around the crack. Then take a piece of brown lunch bag and rub it with glue. Place it over the crack, and rub some glue on it, pressing it in place. The glue should by now soak the paper of the cone and bag. When dried you cant tell the difference in sound and its as sturdy as ever. This also works for those units that a animal (or kid) has put a hole in. I repaired a speaker that was missing almost half of the cone from mice. It sounds great and was cheap to do.

    Comments on speaker driver repair

    (From: Nathan Shinder (alphanathan@netzero.net).)

    When they assemble drivers, they use shim in between the center pole piece and the voice coil to align them. Just get a sheet of plastic that has a good, not tight fit, and make a cylinder. the cylinder can have small gap in it. Also, many times the spider is held in place with contact cement, which can be removed with lacquer thinner. This is better than cutting anything but lacquer thinner WILL eat a foam surround, though not the spider. Rewinding a coil is usually so tight around the for that you can't get it off. more small pieces of shim is the answer, pull those out first. Using slow drying adhesives to reassemble the driver is good, so that the shim in the voice coil will determine the alignment, and not grab with a weird alignment. I built myself a 22" sub DRIVER from other parts, so I know what works. It takes a pounding like anything, and has not come apart in six months of abuse.

    Recommended adhesives and solvents

    (From: Greg (EB) Danner (gdanner@prairienet.org).)

    I've been using surrounds from MAT and also from Dalbani. They are MUCH cheaper than some of the other sources, but appear to be of good quality. What I've been using for glue is:

    1. "Elmer's Craft Bond Tacky Glue". A 4 oz. bottle is about $3.00 from local OSCO drug store, found it in their school and office supply aisle. Nice and thick, stays where you put it, dries quickly, and stays flexible (unlike some white glues which dry hard and brittle and might crack when vibrated in a speaker).

    2. "Weldwood Universal Space Age Adhesive (concentrated)", 4 oz. bottle was about $4.00 at a local hardware store. Thinner and runnier than (1), but also dries flexible, and it supposedly bonds more materials than (1). If you check some of the pictures on the DECWARE speaker repair pages, you will see a bottle of this glue next to the speaker.

    For cleaning off the old glue and bits of old surround, as well as for softening the glue around the dust-cap so it can be non-destructively removed for cleaning the voice coil gap and shimming the voice coil while replacing the surround, the following solvent works great:

    1. "Oatey Cleaner for CPVC or PVC or ABS - Clear", 16 oz can, white and yellow label. Available in plumbing department at local hardware stores. This is a solvent (MEK and acetone) based cleaner, so be sure to follow label directions, as it is flammable and you don't want to inhale the vapors. Just brush it on with a small paint brush, wait 30-60 seconds, and it will soften the old glue so you can peel it off.

    (Portions from: rbeez99@aol.com)

    If you are actually rebuilding the voice coil on a large driver, you really need a high temperature adhesive. Much of that power becomes heat! JB Weld is a good two part Epoxy for this application.

    Some sources for loudspeaker repair parts and services

    Inexpensive speaker refoam kits and other related items can also be found on eBay, often using "Buy-It-Now", at lower prices than from dealers in part because there is no minimum order dollar amount which may greatly exceed the cost of the refoam kit! Search for "speaker refoam" and "speaker foam".

    Most/all of the places below sell speaker refoam kits and other speaker repair parts and accessories, and some offer speaker repair services. (I have not dealt with any of these places personally - they are all based on recommendations of others. Listed alphabetically.)

    Repairing an open driver

    An open driver can sometimes be rescued by tracing the input wires through the cone and under the center protective dome. The most likely places for these wires to break are right at the place where they pass through the cone and just after they pass under the dome. Note: some drivers have replaceable voice coil units. If this is the case, you should probably just replace the entire unit.

    First, scrape away the insulating varnish on the front of the cone where the wires emerge and head toward the center. Use your ohmmeter to test for continuity here. If you find that you now are measuring a reasonable resistance - a few ohms, then trace back to determine which of the two wires is broken or has had the solder connection come loose. If it is still infinite, you will have to go under the dome.

    Use an Xacto knife to carefully remove the dome. Use a shallow angle and cut as near the edge as you can. Take care not to puncture the paper cone which may continue under the dome as the voice coil may be of a smaller diameter than the dome. The shallow cut will also provide a base to reattach the dome if you are successful. Carefully scrape off a bit of the enamel insulation as near to the voice coil as possible and test with your ohmmeter once again. If the resistance is still infinite, there is nothing more you can do but salvage the magnet for fun experiments or erasing floppy disks. There is essentially no way to replace just the voice coil unless your driver has a removable voice coil unit (in which case you would not be reading this).

    If the resistance now measures normal - a few ohms, trace back to determine which wire is broken and use some fine (e.g., #30 gauge) wire to bridge the break. You will have to scrape off the enamel insulation to permit the solder to adhere. Make sure it is secure mechanically first - a speaker cone is a rather violent environment for soldered connections. Finally, use some flexible adhesive to protect and reinforce the solder connections, to glue down your new wire along its entire length, to protect and reinforce the place where the wire passes through the cone, and finally, to reattach the central dome. Let the adhesive dry thoroughly before playing the finale to the 1812 Overture.

    Loudspeakers - repair or replace?

    Assuming that the cabinet is in reasonable condition, the question arises: is it worth replacing broken, damaged, or worn out drivers or faulty crossover components that are not repairable rather than just dumping the speaker systems?

    It is very straightforward to swap drivers as long as you get ones with similar characteristics. It all depends on what you want out of a loudspeaker. If you are basically happy with them, then it will be a lot cheaper than replacing the entire speaker system(s). However, speaker system quality has improved considerably in the last 15 years so now may be the time to upgrade.

    As far as crossover components are concerned, these are basically common electronic parts and replacement is probably worthwhile.

    However, if one driver has a deteriorated suspension, it is likely that its mate does as well and that other drivers may not far behind. Replacing **all** the internal components of a loudspeaker may not be worth it.

    Radio Shack as well as places like MCM Electronics and Dalbani have a variety of replacement drivers, and crossovers and parts.

    Speakers wired in series?

    (From: Frank Fendley (frank.fendley@datacom.iglou.com).)

    Wiring speakers in series increases the impedance of the load, generally allowing less expensive output chips and smaller heatsinks, due to reduced current. It also decreases the amount of output audio power in most cases, since power is inversely proportional to impedance for a given voltage.

    Many cheaper home stereo receiver and power amps are configured in a similar manner. If you have a switch and output connectors for "A" and "B" speakers, in some cases when you turn the switch to "A+B", the two left speakers and the two right speakers are wired in series. To find out if this is the case on your stereo, hook up only one set of speakers to the "A" jacks. Turn the speaker select switch to "A+B". If you have no audio through the speakers, then your receiver or power amp is configured to place the speakers in series with both sets of speakers are connected. On better stereo equipment, if you have only one set of speakers and select the "A+B" switch setting, your speakers will still function, indicating that the speakers are wired in parallel in the "both" position.

    Bottom line - the answer is money (isn't the answer always money?). It's cheaper for the manufacturers to design for speakers in series.

    Comments on speaker shielding

    When loudspeakers - even those little speakers that came with your PC - are near TVs or monitors, there may be problems with the fringe fields of the powerful magnets affecting color purity, convergence, or geometry. Speakers designed to be used with PCs in close proximity to their monitor will likely include some internal shielding. This may even be effective. However, the large powerful loudspeakers used with high performance stereo systems will likely not have such shielding. The best solution where display problems have been traced to the loudspeakers is to move them further away from the TV or monitor (and then degauss the CRT to remove the residual magnetism. Where this is not possible, shielding of the speakers may be possible:

    (Also see the document: TV and Monitor CRT (Picture Tube) Information.)

    (From: Lionel Wagner (ck508@freenet.carleton.ca).)

    Put a Tin can over the magnet. This will reduce the external field by about 50%. If more shielding is desired, put additional cans over the first, in layers, like Russian dolls. (Note: a Tin can is actually made nearly entirely of steel - the term 'Tin' is historical. --- sam)

    (From: Nicholas Bodley (nbodley@tiac.net).)

    While both electrostatic and electromagnetic (E/M) fields can affect the paths of the electron beams in a CRT, only E/M fields are likely to be strong enough to be a problem.

    Magnetic shields have existed for about a century at least. Some decades ago, a tradenamed alloy called Mu-Metal became famous, but it lost its effectiveness when bent or otherwise stressed. Restoring it to usefulness required hydrogen annealing, something rarely done in a home shop (maybe one or two in the USA).

    More-recent alloys are much less fussy; tradenames are Netic and Co-Netic.

    Magnetic shields don't block lines of force; they have high permeability, vastly more than air, and they guide the magnetism around what they are shielding; they make it bypass the protected items.

    I have been around some shielded speakers recently, but never saw any disassembled. They looked conventional, must have had the "giant thick washer" (my term) magnet, and seemed to have a larger front polepiece than usual.

    They had a shielding can around the magnet; there was a gap between the front edge of the can and the polepiece. I suspect that a second internal magnet was placed between the rear of the main magnet and the rear (bottom) of the can, so there would be minimal flux at the gap between the can and the front polepiece. Holding pieces of steel close to the gap between the can and the polepiece showed very little flux there.

    Modern magnets are not easy to demagnetize, in general.

    (From: Dave Roberts (dave@aasl.demon.co.uk).)

    The *good* so-called magnetically screened speakers rely on two means of controlling stray flux. The static field from the magnet on the speaker (which would cause colour purity problems) is minimized by the design of the magnet. This is often at the expense of gap field linearity, leading to greater distortion - not that most users seem to worry about that...

    The mains varying field is minimized by use of a toroidal mains transformer, but the more recent mains powered speakers seem to be coming with *plug top* PSUs, which take the problem further away.

    His need is for loudspeakers already mounted in a wall, not the individual drivers. The assumption is that the woofer/tweeter/whatever are correctly wired inside the enclosure.

    Loudspeaker phasing

    Multiple speakers need to be driven so that they are in phase - positive peaks result in the cones of all drivers moving in the same direction. All drivers are marked in some way with + and -/red and black/etc. This results in the best base response, uniformity of sounds, and stereo imaging.

    (Where you are actually constructing a loudspeaker system from individual drivers, this must be done inside the speaker enclosure as well matching the markings on each of the drivers.)

    If the front cover (grill cloth) is removable or relatively transparent, than it is a simple matter to observe or feel which way the woofer cone moves when a 1.5 V battery is attached to the speaker wires. Make sure both speakers are wired to the amplifier outputs with the same polarity.

    However, once a loudspeaker is mounted in the wall, for example, access to see the markings may not be possible. There may be no markings so it must be an acoustic method I would think - even observing the woofer cone may not be possible.

    One can do this by feeding the same low frequency signal (say 60 Hz) to both channels and positioning a microphone about midway between them (and away from the wall). Then, the correct polarity will have greater amplitude. The acoustic wavelength of a 60 Hz signal is more than 18 feet so precise position shouldn't be critical. This is basically the same way one does phasing by ear except that a scope or sound level meter will be more precise!

    (From: Robert Kesler (kesler@eunet.yu).)

    Such a 'gadget' is available as a commercial instrument for 'synchronizing the polarity' of the speakers, microphones and/or cable polarity in a system, where many microphones amplifiers and speakers are used in each others fields.

    There are two separate units:

    One possible simple way to make the receiver could be to amplify the peak-to-peak value of the received signal to drive a CMOS chip, and feed it in the input of an inverter and in a buffer, the inverter should feed a red LED, the buffer a green LED.

    (From: Jim Coe (jimcoe@ix.netcom.com).)

    1. If you have 2 speakers and you want them in same phase (but you don't care about absolute phase - i.e. whether a positive air pressure at the recording microphone reproduces as a positive air pressure at you ear, not negative) than the idea about measuring by interference 1/2 way between is OK. Except that:

      • If you measure with a microphone and the speakers are in a wall, DO put it against the wall - to get a purer pressure response and to get away from high frequency reflections.

      • Instead of looking for a summation of the pressure waves from the 2 drivers, look for a null zone when one driver is out of phase. A summation cannot be more than +6dB SPL (a "doubling"), but the null can be (theoretically infinite) much more (maybe -12 dBSPL to -30 dBSPL in practice). Once you know the drivers are out of phase, you know how to get them in phase.

    2. If dealing with 1 driver and you can't access the leads and see the cone to use a battery, inject a positive waveform (diode across a sine, triangle or square wave generator? Look at the acoustic wave with a microphone driving an oscilloscope. You can use a small bare speaker, previously tested with a battery while observing the cone, to calibrate your setup. In this way, you can get the absolute phase.

    Should you care about absolute phase? Yes - if you want the best 3-D sound effects. Also, with close microphone recording techniques, some sound sources do not produce symmetrical air pressure waves - so listening in the same phase as the recording can give more realism. That is, if the audio processing between you and the recorded signal doesn't mess things up too much.

    Don't ever trust the markings on speaker terminals from the speaker manufacturers. I was once required to test many drivers from a famous American manufacturer, using a high quality phase tester, and found more than 20% of them mislabeled! They weren't testing them on their assembly line - just marking them by visual inspection of the driver wiring. They later became a customer for the same phase testers I was using (some friends of mine invented it and I was one of their beta testers).

    Electrostatic Loudspeakers and Headphones

    While the vast majority of sound producing devices utilize a moving coil (or at least are magnetically actuated), there are also some that are both very expensive and which supposedly provide very accurate sound reproduction based on electrostatic principles. Basically, a conductive membrane or diaphragm is charged to a high DC voltage with respect to a fixed plate - several hundred volts for a headphone driver but several thousand volts for a wall-size loudspeaker. This sets up a bias field that draws the diaphragms together and keeps them tight. The audio signal is boosted to a high AC voltage and added to the DC bias. The resulting change in force results in the movement of the diaphragm and thus the production of sound. The claimed advantages of such an approach is that the sound emitting area can be very large and the movement very small minimizing various types of distortions.

    The DC bias voltage can be supplied by any number of means - directly from the AC line via a transformer and/or voltage multiplier or using a high frequency inverter. The current requirement is essentially 0.

    (Note: There are also some 'planar magnetic' loudspeakers in existence which may look similar to electrostatic types but have no external power source and special circuitry inside. The planar voice coil is etched onto a thin diaphragm suspended within the magnetic structure.)

    The audio signal from the output of a normal amplifier may be boosted to a higher voltage by another special amplifier which is part of the electrostatic loudspeaker 'energizer' before being further boosted by a transformer to drive the speakers themselves.

    The energizer schematic below is for a pair of Radio Shack electrostatic headphones. A room-size set of Thunderblasters would require a somewhat more sophisticated set of electronics - probably including its own amplifier as well as operating at much higher voltage and higher power - but the basic idea will be the same.

            
                             o--o L Spkr Out            5.1K         1
          Left Chan In o---o                      +-----/\/\---+-----o L Drive
                            \o---/\/\----+---+ ||(             |
                                 3.3     |    )||(             |
                                 PTC  30 /    )||(      100pF _|_
                                      5W \    )|| +--+   500V ---
                                         /    )||(   |         |
                                         |    )||(   |         |
                      o------------------+---+ ||(   |         |     4
                                                  +--|---------+-----o L Ret
                                                     | 
                             o--o R Spkr Out         |  5.1K         3
         Right Chan In o---o                      +--|--/\/\---+-----o R Drive
                            \o---/\/\----+---+ ||(   |         |
                                 3.3     |    )||(   |         |
                                 PTC  30 /    )||(   |  100pF _|_
                                      5W \    )|| +--+   500V ---
                                         /    )||(   |         |
                                         |    )||(   |         |
                      o------------------+---+ ||(   |         |     5
                                                  +--|---------+-----o R Ret
                                                     | 
                   25K            1N4004       5M    |               2
          AC H o---/\/\---+-----+--|>|---+----/\/\---|---------------o Bias Com
                          |     |       _|_   1/2W   | 
                          /     |   1uF ---          | 
                     100K \     |  160V  |           | 
                          /  +--|--------+           | 
                          \  |  |   1uF _|_          | 
                   25K    |  |  |  160V ---          | 
          AC N o---/\/\---+--+  |        |     1M    | 
                                +--|<|---+----/\/\---+
                                  1N4004      1/2W
    
    

    The 3.3 ohm PTC (Positive Temperature Coefficient) thermistors are supposed to provide some sort of protection for the transformer and its circuitry in case the unit is fed with too much power. Now how could that happen? :) However, if abused too much, they can fail as well. Problems may occur in the voltage doubler and high value resistors sometimes just go bad on their own.

    Trying to find replacements can be a treat but it appears that some PolySwitch protectors fit the description and should be available from major electronics distributors. For example, the 3.3 ohm device has a hold current spec of 0.17 A (.1 W) and a trip current of 0.34 A (.4 W). However, I don't know if this is adequate for the headphones described above.

    Comments on electrostatic headphone operation and repair

    (From: bill_h (bill_h@sunsouthwest.com).)

    I have a couple pair of the Radio Shack electrostatics that I've used from time to time over the years (about thirty, I think!)

    When they were closing them out, I ordered a couple spare 'replacement elements', and from looking them over, I think I have some ideas about repairing them, if it ever becomes necessary.

    You'd have to come up with a frame to stretch the mylar. Then you would glue the plastic 'element' frame to it. Don't know how much tension you'd need, but I'm sure it can't have any slack whatever.

    I was thinking about looking for one of those metal silk screen frames that used to be pretty common around circuit board houses. A nice size would be maybe 8'' or 10'' square, so a 'standard' mylar (Saran wrap? (I don't think so, but it might work --- Sam) would fit. Lay a piece onto the frame, clamp it, then tighten the screws to put some tension on the film and make sure it's even (use a torque wrench) and flat.

    After the glue dries, just trim away the excess film. Put the spacer rings and metal plates back and basically you have a new 'element'.

    I'm assuming everybody knows the way these things work - a mylar film is pushed and pulled between a couple highly charged (maybe 300vdc) metal plates, with a lot of holes in them. The mylar moves the air, so you get sound, which has to pass through the metal plates.

    There is one other thing I've noticed. Probably for protection, there's a VERY high value resistor in series with the DC supply, and when the 'phones have been sitting un-energized for a while (weeks/months) they can take a DAY or more to become fully charged. And until they charge, the sound output is VERY LOW.

    In other words, you can't plug Realistic electrostatics in, send audio into them, and tell anything about whether they work or not, for HOURS, at least.

    Over the years I've tried every type of earphone that's come along. While there are some positive things that have come along, for my money nothing has yet equaled a good electrostatic for super clean mid/upper frequencies from the large area (planar) radiator.

    I've long suspected small radiators, trying to move large amounts of air by extreme motion, run into the adiabatic characteristics of air whereby some of that extreme motion is turned into HEAT instead of sound. And that may account for some unpleasant distortion.

    A large area radiator doesn't impart as much force to the air molecules nearest its surface, and doesn't run as much risk of this non-linear effect.

    Might explain the superior sound from large planar speakers like Magnapans.

    With headphones, you don't have a limited 'sweet spot' to worry about.

    Repairing Acoustic Research (AR) Speakers

    The following will also apply to many other brands of loudspeaker systems.

    (From: Jim Adney (jadney@vwtype3.org).)

    You must go in through the front hole that the woofer mounts in. The hard part is removing the grill cloth and its frame without damaging it. Mine have all been glued in place so you have to use a thin piece of metal that you can work around the side and in back and then pull out carefully. Do this carefully all around until you have broken all the glue bonds; the grill cloth frames are usually plastic, so you have to be careful not to break them. You should probably inspect the face of the cloth for staples first, as AR used staples on the AR-2ax's that I have taken apart. If you have staples, just carefully pull them all out from the front and then the grill cloth/frame will come out easily.

    Then you can see all the speakers and you will notice that the woofer is just held in place with a ring of screws. Remove the screws and pry the speaker up (it is sealed in place with a compound that will still be somewhat soft and that you should just reuse when you're done.

    Once the woofer is out, mark which color wire goes to which terminal on the woofer and then unsolder them. They MUST be put back the same way!

    Inside you will find the speaker packed with fiberglass insulation. Carefully pull all this out and pack it in a box or paper bag for reuse later. Note how it is placed so you can do it the same way. I think there was also some kind of paper which was used to keep the fiberglass from rubbing against the backside of the speaker cones. Some kind of disposable gloves might be nice for handling the fiberglass.

    Now you can see the crossover attached to the inside back of the cabinet. Make yourself a sketch of the wiring so that you can put it back the way you found it, and then unsolder the leads to the 2 pots and remove the pots. These disassemble easily, so clean/scrape until they work properly again. You can carefully clean the heavy oxidation off the slider and the wire with a dental tool or a small screwdriver; work slowly and carefully Reassemble and install.

    Put everything back in reverse order. The crossover components all age well, so there is no point in just replacing things because they are old, but if something was obviously burned you might have to think about replacing it. I have never seen anything damaged there.

    When I put these back together I use velcro to hold the grill cloth/frames in place. You can buy velcro by the yard at fabric stores and glue the pieces in place. This makes future repairs MUCH easier.

    I've done about 4 pairs of old AR speakers (2s and 3s) this way so far, and they have all fixed up nicely. My current set of AR-3s needed this when I found them, and they have worked nicely ever since they were repaired, about 8 years ago. Takes an afternoon, no parts required.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Telephone Equipment

    Web resources for telephone information

    In the old days, before dinosaurs and indoor plumbing, there were telephones. You rented your dial phone from the PHONE COMPANY and it came in two styles: desk phone or wall phone. You could have any color as long as it was black. A great advance was the introduction of decorator colors, which was emphasized when you ordered your telephone service. Then came Touch Tone phones but these still looked like phones! And for the most part, all of these were very reliable. A 50 year old phone is very likely to be in perfect operating condition today having never required repair despite long faithful service and much abuse (the PHONE COMPANY made mucho profits from those rentals year in and year out with no expenses!) and only their equipment could be plugged into the phone line. Now with deregulation we have almost every shape, style, color, and quality. Phones are throwaway items given away in cereal boxes. And all types of other equipment gets connected including modems, fax machines, intruder alarms, and college senior projects. Amazingly, the phone system remains very reliable.

    There are some additional Telephone related Web links in my bookmark file at Sam's Neat, Nifty, and Handy Bookmarks.

    Telephone basics

    DTMF codes

    DTMF (Dual Tone Multi-Frequency) are the tones that phones use. The frequencies are as follows:

       Hz     1209   1336  1477   1633
     ----------------------------------
      697       1      2      3     A
      770       4      5      6     B
      852       7      8      9     C
      941       *      0      #     D
    

    Follow the rows and columns to the number you want to know the frequencies of and this table will show you. The column of letters at the right is on some Ham radios.

    Where an old style ATT Touch Tone phone's DTMF frequencies need to be adjusted, accuracy of better than 1 Hz is easily obtained without fancy equipment - just another working tone dialing phone. See the section: Classic ATT Touch Tone phone will not dial properly.

    For more information on DTMF coding, decoding, equipment, chips, etc., see the:

    Phone jack or extension installation or repair

    The phone companies would have you believe that installing or repairing phone wiring is somewhere between rocket science and nuclear physics in complexity. In fact:

    Telephone interference from local radio station

    (From: Robert Myers (rmyers7@ibm.net).)

    See the:

    for an explanation of this problem.

    (From: Gray Frierson Haertig (gfh@haertig.com).)

    AM interference to telephones is very common. Most modern telephones are full of transistors and diodes which make splendid demodulators for the AM signal. Some of these semiconductors are in the part of the circuit that drives the earpiece, which might explain why only you hear the radio. We assume that there is really an 880 AM in your town so we can rule out psychosis. If the radio starts telling you to kill people, get help immediately.

    The AM is probably coming in on the phone lines. The reason phones have this problem in particular, is because they are connected to really long antennas - the phone lines. Bet the 880 transmitter is pretty near your house.

    The susceptibility of different kinds of phones is very different. And, depending on where in the circuit the detection is happening, one susceptible phone can put the AM audio on the phone line so all the phones will have problems. First thing to do is unplug all your phones. Then plug phones in one a time in their normal locations and see which phones are susceptible.

    Check out Mike Sandman's Telecom and Cable Installation Products. These folks make a wide range of interference filters that frequently will help with the problem. It may be cheaper to replace seriously affected phones with phones that are not so susceptible. And remember, the price of the phone has absolutely nothing to do with it's susceptibility.

    (From: Lord Valve (detritus@ix.netcom.com).)

    Your phone wiring has a local ground, usually attached to a water pipe. Chances are better than even that this connection is oxidized. Remove the clamp and clean the copper pipe with a piece of Scotch-Brite. Clean the clamp, too, and the incoming ground wire. Put it all back together and cover the whole assembly with grease. (The grease will block moisture and prevent re-oxidation.)

    (From: Michael Bell (mbell72398@aol.com).)

    I find your post a common problem to an everyday experience to me. I work with a local telco and this is very much a problem. Some phones are more prone to this than others. Believe it or not, the electronic ringing (this is any phone that does not have the plain old bell in it) ones are more likely due to the circuits in them. The phone company will (at no charge to you) put a AM coil that will greatly lessen the interference in the protector outside your home. They should have a that blocks your local AM station's frequency before it comes in your home. However, this will not help if certain phones are acting as the antenae for your interference. Call your local telco first. Why pay if they can solve it.

    Remember that they cannot charge you for work up to the protector.

    (From: Anthony Falvo (afalvo@borg.com).)

    I am the Chief Engineer of an AM radio station. We put out a measly 1000 watts of power but it has the same effect on all of our studio gear. What you need to do is open the affected phone and place a 40 mH coil in line with about .01 uf cap in series across the phone line values may very ans get a coil that is tunable slug like from an old TV IF section wire in series and tune the coil for best rejection of the offending signal you may completly eliminate it sometimes you need 2 of these FILTERS to ground from bolth sides of the phone line depending hoe bad the interfereing signal is what you are essentialy creating is a crude NOTCH filter that will NOTCH out the offending freq according to the Tuning of the coil.

    If I can eliminate the noise from our studio lines wich are no more the 20 feet from the Tower, then I'm sure this will work for you.

    (From: Robert Blackshaw (blackshaw@erols.com).)

    I spent 33 years with Bell Canada and have seen this phenomena in rural areas with open wire lines. The splice connectors would become oxidized (copper oxide) and treat every subscriber to "free" radio.

    (From: Jim Muehlberg (muehlber@plains.nodak.edu)..

    I'm currently in studying EE and took a course in electromagnetic compatibility (EMC) This is a huge field with many employment opportunities.

    We conducted a lab experiment that simulated this problem. It is a fine example of what is called common mode currents. The idea to install the chokes as described above is likely to cure the problem. Perhaps a simpler quick check is to take the phone cord from the wall and wrap as many turns as possible around an IRON bar or big bolt or if you can find one surplus, a big ferrite toroid. It is important that each conductor be wrapped in the same direction. This constitutes a common mode choke. This will be "invisible" to the differential signal (desired) and be a large reactance to the common mode currents. If it works, install the whole shebang at the wire entrance.

    Answering machine comments

    Most answering machines still use one or two tape decks. Most problems are mechanical. Refer to the sections on the relevant tape player/recorder problems. The newest ones are fully digital electronic - forget repairs unless obvious bad connections, physical damage, power supply, or phone line side failure.

    Answering machine delays after playing OGM

    This may be one of those machines where it has to go through the entire outgoing message (OGM) tape before allowing recording of the phone conversation - If it is, then just get yourself the shortest outgoing message tape you can find and time your OGM to nearly fill it.

    Also, if you are trying to use an OGM tape recorded on another answering machine, even if the tape is compatible, the frequency or coding of the control tones - the beeps - may not be the same. Try re-recording it on the machine in question.

    If these are not the problems, the machine may not be sensing the beep code put on the tape when you record the OGM or the beep is not being recorded properly. This is likely an electronic or logic problem requiring the schematic unless you get lucky with bad connections or a broken wire at the tape head.

    Answering machine picks up then hangs up

    Beyond this, circuit diagrams would be a definite plus.

    Answering machine does not complete cycle

    This is often a mechanical problem. As it goes through the cycle, see if the mechanism is perhaps getting hung up at a certain point do to a weak spring or motor. A cam may get stuck or a solenoid may fail to engage. Gently prodding the uncooperative part (or any likely parts if the appropriate one is not obvious) may convince it to continue and allow you to make a diagnosis.

    For endless loop outgoing cassettes make sure that the metal sense strip is not worn off and that the sensor is making good contact. Try a new outgoing message cassette or manually short the sensor contacts to see if it will then shut down.

    Answering machine has weak outgoing message

    You probably have no way of knowing since you probably never listen to the outgoing message, but did the problem happen suddenly?

    Does playback of the outgoing message directly to the speaker appear to be at normal volume?

    Do incoming messaged get recorded at normal volume?

    First, confirm that the unit is in good mechanical condition. See the section: General guide to tape deck cleaning and rubber parts replacement. Clean the tape head and inspect for anything that may be interfering with good tape-head contact. Clean the internal record/play selector switches. Dirty contacts can result in any number of symptoms.

    Assuming that none of this helps significantly, you are left with a problem in the electronics.

    If local record and playback of the the outgoing message works normally, the problem is not a bad tape head. It is probably in the interface to the phone line.

    If local record and/or playback do not work correctly, then there are likely problems with that circuitry.

    One other slight possibility is that you have so much equipment (phones, modems, fax machines, etc.) on the phone line that in your house that the answering machine is not able to drive the line properly and reduced outgoing message volume is the result.

    Newly installed phone will not tone dial

    If a Touch Tone phone that was previously working now does not tone dial from a new jack or new residence (the button presses are totally ignored, but all other functions are unaffected), the red and green wires are probably interchanged at the new jack, or the phone itself is miswired (the wires inside the phone may have been interchanged to compensate for an incorrectly wired jack at the old location).

    Newer electronic phones will utilize either polarity. The older ATT battlewagons will only dial when hooked up with the correct polarity. This does not affect conversation, ring, or rotary phones.

    Cordless phone problems

    There are several types of problems with cordless phones that can be diagnosed and repaired without sophisticated test equipment. Anything involving problems with the RF or digital circuitry is not likely to be within the scope of your capabilities, at least not without complete schematics (yeh, right), test equipment, and a miracle or two.

    1. Bad rechargeable battery - dead, shorted cell(s), or reduced capacity. The NiCd battery packs in cordless phones are usually easily replaced for around $5-10. This really is the best solution. The problem is almost never in the charging circuits. Replacing individual cells is not recommended. Battery packs can be built up from individual NiCd cells with solder tabs for a modest cost savings. Reuse the old battery pack connector (you may need to do this with a replacement pack as well if the new connector is not identical to the old one), double check polarity, and tape and insulate your homemade pack after soldering to prevent shorts.

      A NiCd battery pack with shorted cells will either prevent operation totally or keep the 'battery low' light resulting in a weak, noisy, or intermittent connection. If the voltage measured on the battery pack after 24 hours of charging is less than 1.2 V times the number of cells in the pack, it is most likely bad.

    2. Dirty keypad - resulting in intermittent, incorrect, or no operation of buttons on handset. This may be due to internal migration of some unidentified substance (how else to describe disgusting sticky gunk that has no right being there on multiple samples of the same model phone) or from external spills. If you are lucky, the keypad can be disassembled without resorting to drastic measures. There may be screws or it may snap apart once access is gained to the inside of the handset. Clean contact surfaces on both the rubber button panel (or plastic keys) and the circuit board first with soap and water and then with isopropyl alcohol. Dry thoroughly.

      If the keypad is assembled with 'upset' plastic (fancy term for little melted plastic posts), then you should probably try contact cleaner sprayed as best as possible through any openings before attempting to cut these away since reassembling the keypad without the plastic posts will be difficult. However, I have successfully repaired these by breaking off the tops of the posts to remove the circuit board and rubber keys, and then using a dab of windshield sealer on each post as an adhesive to hold the thing together after cleaning. However, I much prefer screws :-).

    3. Bad AC adapter on base station - see the docuemnt: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs. This will likely result in a dead base station. If you have replaced the AC adapter or are using a universal type, double check the voltage setting AND polarity.

    4. Bad phone line connection - don't ignore this possibility - test with another phone.

    5. Bad circuitry on phone line side of interface (coupling transformer) - inspect for blown or shorted components.

    6. Bad connections or broken circuit board - if the handset has seen violent service, these are likely possibilities. See the section on: "Equipment dropped or abused".

    7. You forgot the code number - some phones use a multidigit code number as a marginal security feature which must match on handset and base station. If the battery goes dead in the handset or the AC adapter is pulled on the base station, this code may be forgotten. You do have the user's manual, right?

      BTW, do set this code to a non-default value. I was once able to dial out on my neighbor's cordless phone using my phone from my house as a result, I suspect, of their phone being set to its default code!

    8. Base station and handset out of sync - some models require that the base station initialize the handset before any communication is possible between them. Put the handset on the base station for a few seconds to reset. This can happen at any time due to circumstances beyond human control but will almost certainly happen if you replace or disconnect the battery in the handset of these model phones.

    Cordless phone keypads

    (From: Martin Sniedze (MSniedze@STRNNTS1.telecom.com.au).)

    I found that the keypad was always getting wet/oily somehow. Cleaning with alcohol only fixed the dialing problem for about a week. A bit of asking at phone repairer revealed that sanyo has a 'possible' problem with the keypads absorbing/emitting the oily substance. The repairer sold me a membrane that goes between the silicon keypad and the PCB, it has carbon pads on the back. It stops the moisture getting through. It has completely fixed the problem in my phone (it was done 6 months ago). They should be free.

    (From: Steve Lenaghan (tamerica@prairie.ca).)

    We do a ton of cordless phones and I have never had to repair a conductive pad in my career (35 years). We soak them in scalding water and dish soap for 30 minutes. I clean the PC boards with alcohol and a rough cloth. Works every time.

    Erratic or noisy telephone equipment

    The following applies to normal desk or wall phones, cordless phones, modems, answering machines, fax machines - essentially anything plugged or wired into the phone system.

    Always check the cords first - especially the one between the handset and the desk or wall phone itself since it gets a lot of abuse. Noisy, intermittent, or totally dead behavior is possible. In some cases, even the (electronics) ringer will not work if a wire in this cord is broken as the ringing signal is generated in the handset and sent back to the ringer unit. Try jiggling the cord at both ends to see if noise is generated or behavior changes. Even permanently wired in cords are replaceable - just take care to draw a diagram and/or label all the wires before disconnecting the old one.

    Bad connections are relatively rare in original ATT dial or Touch Tone telephones. These old phones also used very high quality contacts for the on-hook, dial, and button switches which rarely resulted in problems. However, with the multitude of modern equipment of all degrees of quality, bad connections and dirty or degraded switches and relays are very common.

    The various microswitches and/or relays for on-hook and other functions seem to be particularly prone to degredation if not properly specified in the design. If phone line pickup or mode switching is noisy or erratic, this is a likely cause. Most of these swiches and relays are replaceable although creativity may be required as an exact match may not be easy to locate.

    To assure that the problem is actually with the particular piece of equipment, disconnect other devices on the same telephone line. Aside from the obvious oversight of a phone that has not been hung up, modems or fax machines that are not powered on may load the phone lines excessively. For example, if you have two PCs with modem connections to the same phone line, the signal quality on one of them may degrade to the point of reducing the effective transmission speed, producing an excessive error rate, or not successfully connecting at all if the other is turned off. (They may also behave strangely if the Originate/Answer settings of the modem are set incorrectly - but that is another matter.)

    Checking phones and answering machines for electronic problems

    Most signal problems will be related to failed components on the telephone line side of the coupling transformer including components in the phone line derived power supply (if used). Phone lines are subject to all kinds of abuse including lightning strikes (although something significant may do extensive damage beyond reasonably hope of repair).

    Modem problems

    First, confirm that your modem settings are correct - reset the modem to factory defaults using the Hayes AT commands (e.g., AT&F1) or dip switch settings. Confirm that your software is set up correctly and that there are no IRQ or IO address conflicts.

    If the modem starts to dial but aborts and hangs up, confirm that you do not have the wiring of the 'telco' and 'phone' connectors interchanges.

    Also see the section: Erratic or noisy telephone equipment.

    Since the phone line is subject to all kinds of abuse, most actual problems (that are not software related), will be on the phone line side of the coupling transformer.

    If you have signal problems - a modem will try to dial out but not make its way to the phone line, testing on each side of the couping transformer with a scope or Hi-Z headphones should be able to determine if the problem is on the logic or phone line side of the device.

    Check that the proper AC adapter is being used (if relevant) and that is is putting out the proper voltage. Check the internal power supply components for proper output. They are often common IC regulators like the 7805 and are easily tested. Replacements are inexpensive and plentiful.

    (From: Rick Miller (wizkid@mv.mv.com).)

    First thing to check: almost all modems have a pair of low-value resistors (10-20 ohm) between the phone line and their line transformer.

    I got a 2400 baud voicemail modem for free this way! Repaired an "unrepairable" modem (according to the ACER computer technician! :) )

    Replaced a "booger resister" with a real 1/2 job.... had to work hard to get the leads soldered onto the SMT pads!:)

    (From: Jordan Hazen (jnh@aardvark.cen.ufl.edu).)

    Yes, in my experience you're much more likely to sustain damage from a phone-line surge than anything on the power grid. Modem electronics tend to be more delicate than the stuff in your power supply.

    First thing to check: almost all modems have a pair of low-value resistors (10-20 ohm) between the phone line and their line transformer. These are intended to take the brunt of a lightning hit and protect the electronics upstream. Traditionally, these have been large, high-current resistors (like 1/2 watt), but sometimes now they try to get away with little 1/16-watt surface mount ones that are much more likely to blow. Sometimes it's obvious when the resistors have died, with visible singe marks, pieces blown away(!), etc. Usually these fail as an open, resulting in "NO DIALTONE" on trying to connect.

    Other vulnerable stuff includes the zener diodes intended to clip down incoming ring voltage, on the transformer "primary" (telco) side. These may fail as a short-circuit. The ring-detect optoisolator may also blow, and it can simply be removed if you don't need to take incoming calls.

    One of my modems actually had the line relay's contacts welded together by a lightning hit, so it stayed off-hook constantly! Check the isolation transformer for a open coil on either side. If it's a high-speed modem, be sure to replace blown transformers with one of about the same type & quality... the ones on 2400-baud modems usually had poor frequency response/linearity.

    Any damage beyond the transformer will be hard to repair w/o a schematic, since the surface-mount diodes, transistors, etc. damaged may be hard to ID for replacement on a surface-mount board. Something blown in this area may cause slow/error-prone connections, rather than complete failure. It happened to be with a particularly nasty strike (the one welding the line relay closed), transforming a 33.6k modem into a 4800 :-(

    Oh, and if the modem's completely dead - no response to AT commands-- you're probably out of luck... this means there's damage to the digital logic, and it's invariably the 200-pin custom ASICs that blow rather that 74xxx buffers.

    (From: jlager@tir.com).

    My experiences with the front end of answering machines are welded relay contacts mostly. The symptom is usually holding down the line.

    Testing a Fax machine without a second phone line

    Note: This was written for phone systems in the UK but should apply elsewhere.

    (From: Peter Duck (pduck@zetnet.co.uk).)

    All you need is another fax machine or a computer w/faxmodem and fax software plus a small circuit to simulate the phone-system.

    (This doesn't provide/check 'ringing', so one must tell the receiving end when to Answer/Start, but I use this for modems and/or fax machines.)

    
                           33 ohms        E     C    LED
             o---------+----/\/\----------.     .----|<|-----+-----o(+)
            To         |                  _\___/_            |
          two-way      |                     |               |
          adaptor      +----|<|--|<|---------+-------/\/\----+   PP3 (9V)
          for both      2 X 1N4148-ish       B        3.3k       Battery
           modems
             o-----------------------------------------------------o (-)
    

    The current is approximately 20 ma, so almost any small transistor is OK. Shown for NPN: adapt if you only have a PNP. The LED is optional, but reminds you to unplug things instead of having to buy a new battery each time. :-)

    If you're trying to figure out how it works, the 'constant' current will be such that the (voltage drop across 33 ohms) + Vbe = (2 * (Vf of a diode))

    Though a phone-line would be fed from a 50 V source (in the UK, anyway), all that's needed to keep the modems happy (or fax machine) is some excess over the Vfs of the diode bridges that enable them to cope with either polarity of line-voltage.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Calculators, Clocks, and Watches

    Web site for clock and watch information and repair

    The following Web site has links to lots of clock repair informaion including a repair FAQ, clock/watch companies, and more:

    Problems with calculators

    Small hand held and desk calculators share many of the same afflictions as hand held IR remote controls. In particular, battery and keypad problems are common.

    Caution: many devices using LCD displays utilize a printed flex cable to interconnect the electronics and the display. Often, this is simply glued to the LCD panel and possibly to the logic board as well. The cables are quite fragile and easily torn. They are also easily ripped from the adhesive on the LCD panel or logic board. If the unit is fairly old, this adhesive may be very weak and brittle. Repair or replacement should this occur is virtually impossible. The material used for the conductors is a type of conductive paint that cannot be soldered. It may be possible to use a similar material like the conductive Epoxy used to repair printed circuit boards but this would be extremely tedious painstaking work. Be extremely careful when moving any of the internal components - LCD, logic board, keyboard, battery holder/pack, and printer.

    The following problems are likely:

    1. Batteries - one or more cells are dead, weak, or have leaked. Try a new set if normal primary cells (e.g., alkaline) are used. Clean the battery contacts. Where rechargeable (usually NiCd) batteries are used, one or more cells may have shorted resulting in a dead calculator or dim display, or printer that doesn't work reliably. See the chapter: "Batteries". Test each cell after charging for the recommended time or overnight. NiCd cells should be about 1.2 V when fully charged. If any are 0 V, the cell is shorted. This is particularly likely with a unit that has been left in a closet unused for an extended period of time. It is generally recommended that the entire battery pack be replaced rather than a single cell as the others are probably on their way out and the capacities will not be equalized anyhow. Rechargeable batteries may be the cause of a calculator that does not work properly on AC power as well since they are usually used like a large filter capacitor and shorted cells will prevent the required DC voltage from being provided to the electronics. Open cells or bad battery connections will prevent this filtering as well and may result in erratic operation or other symptoms. For this reason, it may not be possible to run a unit of this type reliably or at all with the rechargeable batteries removed.

      Some calculators that use rechargeable batteries like older HPs and TIs have a battery pack of 24.4 to 3.6 V with a DC-DC inverter to obtain the 9 V or so that the NMOS chipset required. These rarely fail except possibly due to leakage of neglected dead batteries. However, good batteries need to be in place for the calculator to work properly. If you are not interested in using these types of calculators on batteries, disconnect the DC=DC convertor and substitute a suitable AC adapter. Check the voltage and current requirements for your particular model.

    2. Keypad - dirt, gunk, and wear may result in one or more keys that are intermittent or bounce (result in multiple entries). Disassemble, clean and restore the conductive coating if necessary. See the document: Notes on the Troubleshooting and Repair of Hand Held Remote Controls.

    3. Printer (where applicable) - in addition to replacing the ribbon when the print quality deteriorates, cleaning and lubrication may be needed periodically. Dust, dirt, and paper particles collect and gum up the works. Clean and then relube with light machine oil or grease as appropriate. Sometimes, gears or other parts break resulting in erratic operation or paper or other jams. Locating service parts is virtually impossible.

    4. AC adapter - if the calculator does not work when plugged into the AC line, this may be defective - broken wires at either end of the cord are very common. However, shorted cells in an internal NiCd battery will likely prevent the proper voltage from being supplied to the electronics even when using AC power since the battery is often used like a large filter capacitor at the same time it is being charged. Open cells or bad connections to the battery pack may result in erratic operation or other symptoms as well.

      Don't overlook the obvious: are you using the proper adapter and if it is a universal type, is the polarity and voltage set correctly? Check the specifications. With the proliferation of AC adapters, it is all to easy to accidentally substitute one from another device.

    Repairing a calculator (or other device) with a fried power transformer

    There may be a thermal fuse (under the outer layers of insulation, between the bobbin and core, or molded into the bobbin) which is the only casualty and it may be replaceable but don't just bypass it (except for testing), so this is worth checking out. Also see the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

    (The specific example below is for a Sharp desktop calculator, model CS-1608. It has a power transformer with 6 wires on the secondary: 2 red, 2 yellow, 1 orange, and 1 brown.)

    Power surges, overheating, or connecting a 115 V device to a 220 V line can all blow the primary. An overload could also but is likely not the problem. In my experience, it seems that the transformers in these things are designed so close to core saturation that excess voltage will not be transferred to the secondary and even plugging a 115 transformer device like a digital clock into a 220 line will not kill the logic, but just melts the transformer primary. I have a bag full of the things (including a cordless phone) which were damaged in this manner when someone decided to do a little house rewiring. You can guess the rest.

    As far as the calculator goes, there are probably 2 sets of secondary windings probably with centertaps - check it with a multimeter. I would guess that the brown is the centertap for the reds and the orange is the centertap for the yellows but simple tests will confirm or refute this. One may be for the logic and the other for the printer motors, LCD, who knows?

    Obviously, if you can obtain an exact replacement, **this** is truly the best solution. Short of this, try to find someone who can measure the secondary voltages on a working model of this calculator. Then, you could replace the transformer with a pair of readily available transformers with suitable ratings.

    If you feel on the lucky side and can at least determine which wires go with which windings, you could carefully bring up power on one output and see if there is any response. It will be at least 5 V. Examining the regulation circuitry and filter capacitors could also provide a clue. Also, you could determine the ratio of the secondaries by powering one from a low voltage AC source and measuring the output of the other (assuming the primary isn't so messed up as to load down the transformer due to shorts).

    There are many options besides giving up.

    Getting inside calculators

    Many will have a couple of screws (possibly hidden under rubber feet or inside the battery compartment) or snaps which will permit the two halves of the case to be separated. However, some very popular models are apparently not designed to be repaired at all:

    Note: I have heard that there is a somewhat less destructive (but not any easier) procedure for getting inside HP48s than that given below but have not seen it.

    (From: A.R. Duell (ard12@eng.cam.ac.uk).)

    Have you ever tried to open up an HP48 (or just about any HP calculator later than the 71B)? It's non-trivial to do non-destructively - these darn things are held together by pegs that were melted over after the case was assembled.

    From memory (and I've never actually done a 48, just the smaller ones) you have to:

    1. Remove batteries, cards, etc.

    2. Carefully peel off the metal overlay on the keyboard. This can be done without putting a fold in it, but it takes practice.

    3. Use a 4 mm (I think) drill held in the fingers to remove the tops of the moulded studs holding the case together

    4. Pull off the back part of the case.

    You can now see the circuit board. It's held down by twisted metal tabs. The keyboard is under it, and is held together by a lot more of those infernal moulded studs.

    Battery powered digital clock problems

    First, try a fresh battery and clean the battery contacts if necessary. If the battery is very low or dead, well.... When the battery is low or the connections are bad, the countdown logic may run erratically - fast as well as slow. Give it a week and then see if the problem still exists.

    If it does - and the error is only a few minutes a week - then an adjustment may be all that is needed. If the error is much worse - like it is running at half speed - then there is a problem in the logic - time for new clock (or at least a new movement).

    There should be a recessed screw for fine speed adjustment accessible from the back - possibly after a sticker or outer cover is removed. It may be marked with a couple of arrows and if you are lucky, with the proper direction for speed increase and decrease.

    Without test equipment, the best you can do is a trial and error approach. Turn the screw just the tiniest bit in the appropriate direction. If this is not marked, use counterclockwise to slow it down and vice-versa.

    Wait a week, then readjust if necessary.

    If you have frequency counter with a time period mode, you can try putting it across the solenoid terminals and adjusting for exactly 1.000000 second. Hopefully the load of the counter will not affect the oscillator frequency.

    With sensitive equipment, it may even be possible to do this without any connections by detecting the fundamental frequency radiation of the quartz crystal oscillator and adjusting it for exactly 32,768 Hz (most common).

    However, keep in mind that the clock's quartz crystal accuracy required to gain or lose less than 1 minute a month is about +/- 1 part in 43,000 which may be better than that of your frequency counter's timebase. One alternative is to perform the same measurement on a clock that is known to be accurate and then match the one you are adjusting to that.

    AC powered digital clock problems

    Common problems include totally dead, missing segments in display, running at the wrong rate, switches or buttons do not work. (Also applies to the clock portions of clock radios.)

    Note that these is often a battery - possibly just an 9V alkaline type for backup in the event of a power failure. If this is missing or dead, any momentary power interruption will reset the clock.

    Although a totally dead clock could be caused by a logic failure, the most likely problem is in the power supply. The power transformer may have an open winding or there may a bad connection elsewhere. A diode may be defective or a capacitor may be dried up.

    Often, the secondary of the power transformer is center tapped - test both sides with a multimeter on its AC scale. Typical values are 6-15 VRMS. If both sides are dead, then the primary is likely open. There may be a blown fusable resistor under the coil wrappings but a burnt out primary is likely. Although generic replacement transformers are available you will have two problems: determining the exact voltage and current requirements (though these are not usually critical) and obtaining a suitable regulatory (UL. CE, etc) approved transformer - required for fire safety reasons.

    If the transformer checks out, trace the circuit to locate the DC outputs. These power supplies are usually pretty simple and it should be easy to locate any problems.

    Missing segments in the display are most likely caused by bad connections. Try prodding and twisting the circuit board and inspect for cold solder joints.

    A clock that runs slow on 50 Hz power or fast on 60 Hz power may not be compatible with the local line frequency since these clocks usually use the power line for timing rather than a quartz crystal. This is actually a more precise (as well as less expensive) approach as the power line frequency long term accuracy is nearly perfect. Sometimes there is a switch or jumper to select the line frequency.

    Dirty switches and buttons can be cleaned using a spray contact cleaner.

    Analog AC Motor Driven Clock Doesn't Run

    These might be found in older clock radios, ranges, ovens, and other similar applicances from a few decades ago.

    The most common type uses a sealed rotor/gearbox inside a AC line powered coil. After 40+ years, even these reliable devices may stop running, often following a power interruption.

    It's most likely gummed up lubricant but probably in good condition otherwise. The best option short of replacement (which may or may not be possible given its age) is to disassemble the gearbox and clean the gear-train and rotor bearings with degreaser, then lubricate the rotor bearings and gears with light oil. To get inside, file along the edge where it's joined, then glue back together.

    Another option if you're lazy, which may not work as well, is to drill a tiny hole in from the side so it just breaks through, and squirt in some degreaser. Let it do its thing, blow it out, repeat a couple times. Then add some light oil and seal the hole. The problem with this approach is that it may not get to the rotor bearings - which are likely the main source of the problem.

    In any case, DO NOT USE WD40 for the lube!!!! You'll just be doing it again in 6 months.

    See Timepiece Workshop Tips and specifically Comments on Telechron Rotor Repair for some specific notes on dealing with the most popular types of movements.

    (From: Jim Adney (jadney@vwtype3.org).)

    The best cure for sticky electric clockworks that I've heard came from the USENET newsgroup for antiques. One person there suggested putting some rather heavy oil in a container and heating it up on the stove.

    Drop the sealed clockworks in the hot oil and let it come up to temp. As it does, the air inside it will expand and bubble out. Wait for the bubbles to stop.

    Remove the container from the heat and let it cool down with the clockworks still in it. As everything cools, the air in the clockworks will contract, pulling oil inside. Let it cool overnight and them pull out the works and wipe it off. Power it up and see if it wants to run.

    Most of the time this will fix things, but you may want to let the works sit on a rag for a week to let excess oil seep out before you reinstall it.

    Once you've oiled it this way, it's a good idea to run it for awhile in various positions other than the one where it spent most of its life.

    (From: Bill Jeffrey (wjeffrey@cox.net).)

    For the clocks in clock radios (similar, I would expect), the standard fix is to drill a tiny hole in the back of the gear case/can, squirt in a few drops of very light oil, or even kerosene, shake it around a bit, and then plug it in and turn it upside down. Leave it upside down, trying to run, for a few days. If it starts, continue to let it run upside down for a few days.

    The problem being addressed is that the original lube gradually runs to the bottom of the case, leaving a very thin coating on the gears, which eventually turns gluey. The new lube tends to dissolve the "glue", freeing the mechanism. Running it upside down eventually redistributes whatever old grease gets thinned out by the new oil.

    Why is my $2 LED clock so much more accurate than the clock in my $2,000 PC?

    Computer clocks use a crystal and are not tied to the AC line - after all, they have to keep time even when the computer is unplugged. Cheap digital clocks that plug into the AC line are extremely accurate - better than anything else you are likely to have access to short of the broadcast time signal.

    The reason for this is that the power line frequency is referenced to an atomic clock somewhere and its long term accuracy is therefore maintained to great precision. Even the short term frequency stability is very good, changing by at most a small fraction of 1 percent due to variations in electric load affecting generator speed (U.S national power grid - isolated areas with local power generators could see much much wider swings).

    These clocks may not keep good time if (1) the power line is very noisy, (2) there is a power outage, or (3) they are broken. Power line noise on the same circuit might confuse some clocks, however. This might happen with light dimmers or universal motors (e.g., vacuum cleaners, electric drills, etc.) on the same circuit.

    Replacing batteries in digital watches

    About the only type of service you can expect to perform is battery replacement but even this can save a few dollars compared to taking the watch to a jeweler. The typical watch battery will last anywhere from a year (alkaline) to 5 years (lithium). The most likely cause of a watch that has a dead or weak display, or has stopped or is not keeping proper time is a weak or dead battery.

    The batteries (actually single cells) used in most modern watches (they used to be called electric watches, remember the Accutron?) are either alkaline or lithium button cells. Some are quite tiny. You will need to open up the watch to identify the type so that a replacement can be obtained.

    How you go about doing this will depend on the watch:

    1. Screws. If there are visible screws on either the front or rear, then removing these will probably enable the cover to be popped off. These will be teeny tiny star (sort of Philips) head type - use a precision jeweler's screwdriver with a Philips head tip. Immediately put the screws into a pill bottle or film canister - they seem to evaporate on their own.

      Note the orientation of the back: The piezo transducer of the audible alarm may make contact via tiny springs in a specific location. Take care not to lose the springs (or put them in a safe place) if they are not secured inside the watch.

    2. Snap off back. This is probably most common. Look for an indentation around the edge. Using a penknife or other similar relatively sharp edged tool in this indentation or at any convenient spot if there is none. It is best to use the wristband mounting rod as a lever fulcrum if possible. The back should pop off. Note the orientation of the back before you set it aside so that you can get it back the same way.

      Same precautions as above.

    3. Cover unscrews. The entire back may be mounted in a screw thread around its edge in which case you will have to somehow grab the entire back and rotate counter clockwise. An adjustable wrench with some tape to protect the finish on the watch may work.

    If there is an O-ring seal (like on the space shuttle), be careful not to nick or otherwise damage it (you know what happens when these are damaged!).

    Once the back is off, you will see a lot of precision stuff - though not nearly as much as in an old fashioned mechanical watch. DON'T TOUCH! You are interested in only one thing - the battery. Sometimes, once the back is off, the button cell will simply drop out as there is no other fastener. In other cases, one or two more teeny tiny screws will hold it in places. Carefully remove these and the button cell. Replace the screws so you will not loose them. Make a note of the orientation of the button cell - it is almost always smooth side out but perhaps not in every case.

    Test the battery with a multimeter. The voltage of a fresh battery will be about 1.5 V for an alkaline cell and as high as 3 V for a lithium cell. A watch will typically still work with a battery that has gone down to as little as half its rated voltage.

    Replacement batteries can be obtained from Radio Shack, some supermarkets, large drug outlets, electronic distributors, or mail order parts suppliers. Most likely, you will need to cross reference the teeny tiny markings on the old battery - places that sell batteries usually have a replacement guide.

    Cost should be about $2.00 for a typical alkaline cell and slightly more for the longer lived lithium variety.

    Note: some watches bury the battery inside the works requiring further disassembly. This is usually straightforward but will require additional steps and some added risk of totally screwing it up.

    Install and secure the replacement battery and immediately confirm that the display is alive or the second hand is moving. If it is not, double check polarity. Sometimes, the back will need to be in place for proper contact to be made.

    Replace the contact springs for the piezo beeper (if present). Where the back can be secured in more than one orientation, make sure it is the same as it was originally. If not, the audible alarm may not work as noted above. There is usually an obvious correct orientation based on labeling or some other means.

    Repairing a watch electromagnet coil?

    This is somewhat unlikely unless you touch or breath on the coil while changing the battery (almost - the wire is VERY thin) but I couldn't resist including it!

    "I have a 70's sonic oscillator watch (Omega 720) that has a bad magnet coil. The leads from the coil are apparently severed from the board. Is there anyone out there that could possibly repair it? (I don't know of any available spare parts."

    (From: Jack Schidt (jack@wintel.net).)

    I collect old Accutrons, and have seen this before. If you genuinely believe the coil itself is OK you can remove the coil, and under a magnifying glass attach a fine strand of wire to the fractured lead near the bobbin.

    You can get this wire from an old ferrite loopstick, etc., Try to find the copper foil Litz type WITHOUT fabric inside- fabric burns easily.

    Do both leads while you are at it. Prior to soldering, wind the new wire around a pin, to give it a small coil. This prevents breakage from happening again. Likely Omega forgot to do this when they manufactured the watch.

    A light touch with a hot iron will remove the insulation on the existing magnet wire. Put a dot of epoxy at the solder joints to prevent more breakage. Tack the new wire to the coil body.

    This is delicate surgery. If you cannot get at enough wire to solder, unwind a turn [if the break is on the outside wire]. If the break is on the inside lead- you may be screwed.

    Lastly, these things are wound with #40 [sometimes smaller- check with gauge] wire, which is fragile, but obtainable. You can rewind the coil- but this takes time. Count the turns while unwinding.

    I do not know of anyone who has a jig to rewind these things. Perhaps a search of the web would turn up something. Have you sent Mike Murray (www.accutronman.com) an e-mail? He may be able to help you. He regularly posts on the alt.horology newsgroup, and those people could help you as well. Perhaps rec.antiques.radio+phono could help. Old radios have IF coils that need to be repaired, and someone there may have a jig.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Photographic Equipment

    Note: For information on electronic flash operation and problems, refer to Electronic Flash Units and Strobe Lights.

    Light meters

    First check the batteries (if any). Self powered meters like the old Westons and their clones could also cause damage to the delicate meter movement if the light regulating lid was left open in bright light. Bad connections were also common. I have repaired the meter movements on these but it is not much fun. See the sections starting with: Analog Panel Meters for repair information.

    Hand held light meters are subject to damage from being dropped.

    Problems with internal light meters include bad batteries and corroded battery contacts, dirty or worn potentiometers.

    Pocket camera repair

    It seems that in the last few years, the amount of circuitry crammed into a compact 35 mm camera has grown exponentially. Auto-film-advance, auto- exposure, auto-film speed detection and loading, auto focus, auto-flash selection, auto-red-eye reduction - just about everything that could be put under computer control has been. Next thing you know, the photographer will be replaced with a auto-robot!

    For the most part, modern cameras are very reliable. However, when something goes wrong, it is virtually impossible to attempt repair for two reasons:

    1. The circuitry is so crammed into a tiny case that access is difficult and convoluted. Many connections are made with relatively fragile flexible printed cables and getting at certain parts means removing a whole bunch of other stuff.

    2. Much of the circuitry is surface mount and many custom parts are used. Schematics are nearly impossible to obtain and with all the computer control, probably not that useful in any case. Most parts are not available except from the manufacturer and then possibly only to authorized service centers.

    However, some problems can be addressed without resorting to the camera repair shop or dumpster.

    If the camera is still under warranty, don't even think about attempting any kind of repair unless it is just a bad battery. Almost certainly, evidence of your efforts will be all too visible - mangled miniature screw heads and damaged plastic seams - at the very least. There are no easy repair solutions. Let the professionals deal with it.

    If out of warranty and/or you don't care about it and/or you want an excuse to buy a new camera, then you may be able to fix certain (very limited) types of problems.

    Getting inside a pocket camera

    For anything beyond the battery, you will need to get inside. However, before you expend a lot of effort on a hopeless cause consider that unless you see something obvious - a broken connection, bent or dirty switch contact, or a motor or other mechanical part that is stuck, binding, or in need of cleaning and lubrication - there is not a lot you will likely be able to do. One exception is with respect to the electronic flash which is usually relatively self contained and simple enough to be successfully repaired without a schematic.

    As with other consumer electronic equipment, getting inside may be a challenge worthy of Sherlock Holmes. In addition to many obvious very tiny screws around the periphery, there may be hidden screws inside the battery compartment and under the hand grip (carefully peel it back if that area is the last holdout). Also see the section: Getting inside consumer electronic equipment.

    This is the time to make careful notes and put all the tiny parts in storage containers as soon as they are removed. If you never follow any of these recommendations for other types of equipment, at least do so for pocket cameras!

    Caution: the energy storage capacitor for the electronic flash may be located in an unexpected spot way on the other side of the camera. Accidentally touching its terminals when charged will be unpleasant to say the least. Even if the camera is 'off', some designs maintain this capacitor at full charge. In addition, it may retain a painful charge for days - with the battery removed. Once you get the skins off of the camera (if you ever succeed), identify this capacitor - it will be about the size of a AA battery - and put electrical tape over its terminals.

    Pocket camera problems

    The following malfunctions may sometimes be successfully dealt with without an army of camera repair technicians at your disposal:

    Caution: never open the back of a 35 mm camera anywhere there is light of any kind if there is a chance that there is film inside. If the camera is dead, there may be no way of knowing. Doing this even for an instant may ruin all of the film that has been exposed and two (usually) additional pictures. Opening the back of any other kind of roll film camera will only expose a few frames as the exposed film usually has a backing (120) or is inside a cartridge (110).

    If a 35 mm camera failed with a roll of film on which you have taken irreplaceable photographs inside, the pictures can still be saved even if the camera never works again. First, wash your hands thoroughly to remove skin oils. Use a closet with a tightly fitting door (at night is better or stuff something in any cracks to block all light - it must be pitch black) for a darkroom. Open the back of the camera and carefully remove the film cassette. Gently pull the exposed film from the takeup spool (on the shutter release side of the camera). It should unwind easily. Avoid touching the film surface itself with your fingers (the edges are ok). Then, turn the plastic shaft sticking out of the film cassette clockwise to wind the exposed film entirely into the cassette.

    (For items (2)-(4), you will need to get inside of the camera. See the section below: "Getting inside a pocket camera".)

    1. General erratic or sluggish operation, weak display, camera pooped out during film advance or rewind. Most likely cause: the battery died.

      Test the battery and/or try a new one. It is possible that the battery simply decided to go flat at an inconvenient time or that a replacement was defective. If possible, check the voltage on the battery while it is in the camera and the affected operations are performed. If the voltage drops substantially, there could be an overload - a motor that is binding or a shorted component. If the camera had been dropped, a mechanical problem is likely.

    2. Flash inoperative or excess current drain - runs down batteries. Other functions may or may not work correctly. Most likely cause: a shorted inverter transistor. The electronic flash or strobe is usually a self contained module near the actual flash window but the energy storage capacitor may be mounted elsewhere - like the opposite side of the case. See the warning below - you could be in for a surprise!

    3. Mechanical problems with focus, exposure, film advance, or rewind. Likely causes: binding due to damage from being bumped or dropped, bad or erratic motor operation, gummed up lubrication or dirt, or defective driver or control logic. Locate the motor for each function (right, good luck) and confirm that they spin freely and move the appropriate gears, levers, cogs, wheels, or whatever. If there is any significant resistance to movement, attempt to determine if it is simply a lubrication problem or if something is stuck. Test the motors - see the section: Small motors in consumer electronic equipment.

    4. Auto-film-loading, film advance, or rewind do not operate at all or do not terminate. Most likely cause: defective motor or mechanical problems, dirty, corroded, or faulty sensor switches or bad controller. If there is no action or something seems to get stuck or sounds like it is struggling, check the battery and motor (see (1) and (3) above). Inspect the various microswitches for broken actuators, bent or deformed contacts, or something stuck in them like a bit of film that broke away from the roll. Dirt may be preventing a key contact closure. Sometimes, improper cable routing during manufacture can interfere with the free movement of a leaf type contact.

    5. Exposure too light or too dark. Check the film speed setting and/or clean the contact fingers under the cassette that sense the film (ASA or ISO) speed. Clean the light meter sensor. Check the batteries, Look for evidence of problems with the lens iris and/or shutter mechanism. If the shutter speed can be set manually, see the section: Testing of camera shutter speed.

    6. Automatic camera not responding to adjustments. Changing the diaphragm or shutter speed usually moves a variable resistor which is part of the exposure computer. If a single control has an erratic effect or no effect, its variable resistor is likely dirty or broken. If none of the controls behave as expected, there may be a problem in the actual circuitry that computes the exposure. There is little chance that you could repair such a fault. First, replace the batteries. Some of these systems will behave strangely if the batteries are weak.

    Unless there is something obvious - the diaphragm control is not engaging the lever of the variable resistor, for example, and you care about the future health of your camera, my recommendation would be to take it in for professional service.

    To successfully repair modern sophisticated compact cameras requires that you be really really experienced working on teeny tiny mechanisms, have the proper precision tools (e.g., good quality jeweler's screwdrivers, not just the $2 K-Mart assortment), bright light and a good magnifier, and a great deal of patience and attention to detail.

    Testing of camera shutter speed

    If you suspect shutter speed problems, there are several easy ways to measure this for your camera. The most accurate require some test equipment but you can get a pretty good idea with little or no equipment beyond a stopwatch (for slow shutter speeds - above 1/2 to 1 second and a TV (for fast shutter speeds - below about 1/60 of a second (NTSC 525/60).

    Some of these approaches assume that you have access to the film plane of the camera - this may be tough with many highly automated compact cameras which will be unhappy unless a roll of film is properly loaded with the back door closed.

    Note that the behavior of focal plane and leaf (in-the-lens) shutters is significantly different at high shutter speeds and this affects the the interpretation of measurements.

    Some simple homemade equipment will enable testing of the intermediate shutter speeds.

    1. Testing slow to medium shutter speeds - the use of a stopwatch is self evident for really long times (greater than .5 second or so). However, viewing or photographing the sweep hand of a mechanical stop watch or a homemade motor driven rotating white spot or LED can provide quite accurate results. Accurate timing motors are inexpensive and readily available. Mount a black disk with a single small white spot at its edge on the motor shaft and mark some graduations around its perimeter on a stationary back board. For a high tech look, use an LED instead. Use your creativity.

      Making measurements from the photographic images of the arcs formed by the spot as it rotates while the shutter is open should result in accuracies better than 1 or 2% for shutter speeds comparable to or slower than the rotation frequency of the motor. In other words, shutter speeds down to 1/10th of a second for a 600 rpm (10 rps) motor or down to 1/60th of a second for a 3600 rpm (60 rps) motor.

      At these speeds, focal plane and leaf shutters should result in similar results since the open and close times are small compared to the total exposure time.

    2. Testing fast shutter speeds - view a TV (B/W is fine) screen on a piece of ground glass at the focal plane or take a series of snapshots of a TV screen (a well adjusted B/W TV is best as the individual scan lines will be visible).

      Note: If your camera has a focal plane shutter (e.g., 35 mm SLRs), orient the camera so that the shutter curtain travels across - horizontally (rather than up or down).

      If you are photographing the screen, take a few shots at each speed in case the timing of your trigger finger is not quite precise and you cross the vertical blanking period with some of them. This will also allow you to identify and quantify any variations in shutter speed that may be present from shot-to-shot.

      • For a focal plane shutter, you will see a bright diagonal bar. (The angle of the bar can be used to estimate the speed of the shutter curtain's traversal.)

      • For a leaf (in-the-lens) shutter, you will see a bright horizontal bar. but the start and end of the exposure (top and bottom of the bar) will be somewhat fuzzy due to the non-zero time it takes to open and close the shutter leaves. You will have to estimate the locations of the 'full width half maximum' for each speed.

      In both cases, there will some additional smearing at the bottom of the bar due to the persistence of the CRT phosphors.

      The effective exposure time can then be calculated by multiplying the number of scan lines in the bar at any given horizontal position by 63.5 uS (the NTSC horizontal scan time).

      If you cannot resolve individual scan lines, figure that a typical over- scanned (NTSC) TV screen has 420-440 visible lines. If you can adjust your TV (remember this can be an old B/W set when knobs were knobs!) for underscan, about 488 or so active video lines will be visible.

    If you have an oscilloscope or electronic counter/timer, fairly accurate measurements can be made at all shutter speeds using a bright light and a photodetector circuit.

    1. Using an electronic counter/timer or oscilloscope. A gated 24 bit counter clocked at 1 MHz would permit (ideally) testing shutter speeds from 1/2000th second to 16 seconds with an accuracy of better than .2 percent. Of course in practice, the finite size of any photodiode and/or the finite open/close time of any shutter will limit this at high shutter speeds. Any resonably well calibrated oscilloscope will be accurate enough for shutter speed determination.

      Construct the IR detector circuit described in the document: Notes on the Troubleshooting and Repair of Hand Held Remote Controls. (Note that the fact that it is called an IR detector is irrelevant since the typical photodiode is sensitive to visible wavelengths of light as well.) Connect its output to the minus gate of your counter or the vertical input of your scope. Put a diffuse light source (i.e., light bulb) close to the lens so that it is not in focus. Position the detector photodiode in the center of the focal plane - mount it on a little piece of cardboard that fits on the film guide rails. Using this setup, it should be a simple matter to measure the shutter timing. Take multiple 'exposures' to identify and quantify any variations in shutter speed that may be present from shot-to-shot.

      • For a focal plane shutter, the time response will be the convolution of the photodetector area and the slit in the shutter curtain. The smaller the aperture of the photodiode, the less this will be a factor. Masking it with black tape may be desirable when testing fast shutter speeds. In simple terms, make the photodiode aperture narrow.

      • For between-the-lens shutters, the finite open and close times of the leaves will show up on the oscilloscope in the rise and fall times of the trace. The measurement on the electronic timer will be affected by its trigger level setting for this reason. However, since this photodetector is not linearly calibrated, the open and close times cannot be accurately determined from the waveform.

    Here's an approach that finally represents a good use for your sound card:

    (From: Jim Busse (busseja@yahoo.com).)

    I thought I'd share a very easy way to measure the speed of a camera shutter using your computer.

    1. Go down to your friendly parts store and get a photodiode. It really doesn't matter which one so long as it is small.

    2. Put a current limiting resistor in series with the diode (100 to 500 ohms should work fine.

    3. Paste the diode on a thin strip of cardboard sized so that the cardboard fits where your film is within the camera. The diode should be placed about in the center as seen from the front of the camera looking through the lens opening. This is not critical but the diode must be placed somewhere the film is exposed to the light when the lens activates.

    4. Use thin wires and connect them to your microphone input on your sound card.

    5. Close the camera, cock the shutter and point the camera at a light source.

    6. If you have Wave Studio (comes with Sound Blaster), start to record the mic input and simply take a picture.

    7. Look at the waveform of the picture. You can set the recording to 44 kB/s so you can easily measure 1/1000s, or 1/2000s exposure.

    The whole setup costs a couple of dollars and gives you instant information. Of course it is difficult to adjust the exposure time for a camera but you can easily compensate using the exposure f-stop, (slow speed, larger opening, etc.).

    Darkroom timers

    Developing timers only provide a display or clock face (possibly with an alarm) while enlarging timers include a pair of switched outlets - one for the enlarger and the other for the safe light. These are usually self resetting to permit multiple prints to be made at the same exposure time setting.

    Where the device plugged into a controlled outlet does not come on, first make sure these units are operational (i.e., the bulbs of the enlarger and/or safelight are not burned out and that their power switches are in the 'on' position. The problem could also be that one of these devices is defective as well.

    Two types of designs are common:

    1. Electromechanical - using an AC timing motor and gear train with cam operated switches controlling the output circuits directly or via relays.

      If the hands fail to move or it does not reset properly, the timing motor or other mechanical parts may require cleaning and lubrication. The motor may be inoperative due to open or shorted windings. See the section: Small motors in consumer electronic equipment. Where the timer appears to work but the controlled outlets (e.g., enlarger and safe light) do not go on oroff, check for a loose cam or bent linkages and dirty or worn switch or relay contacts. If the dial fails to reset after the cycle completes, it may be binding or require cleaning and lubrication or a spring may have come loose or broken.

    2. Electronic - digital countdown circuits and logic controlling mechanical or solid state relays or triacs.

      Where the unit appears dead, test as with AC line powered digital clocks (see the section: AC powered digital clock problems). If the buttons have the proper effect and the digits count properly but the external circuits are not switching, then test for problems in the power control circuits. If the unit is erratic or does not properly count or reset, there could be power supply or logic problems.

    Weird exposure meter problem of the year

    Here is one for the photo album:

    "Ever since I bought the Mamiya 645 Pro 2 months ago, I've had exposure problems. I usually bring any new eqpt up to Twin Peaks (in SF) to test for lens sharpness, and overall function. Well my first shots from there were 2 stops overexposed, and the meter was reading wrong, so I returned the camera for repair, assuming it was broken out of the box. Mamiya went over it with a fine tooth comb, and could find nothing wrong with it. I got it back on Monday, and went up to Twin Peaks again. Same problem as before! The meter read 2 stops over! I cursed the techies at Mamiya, I cursed the product, I cursed MF, and then I decided to get scientific about it. So I took the camera off the tripod, and pointed it around at various things: all normal readings.

    I pointed the camera back at the scene I had just metered on the tripod...normal reading. I remounted the camera on the tripod ... 2 stops over. I removed the camera ... normal reading. I remounted the camera ... 2 stops over. Unbelievable. So that's when I started thinking about the RF and TV signals being transmitted from the big tower there, and how the tripod might act as an antenna, and cause a small current to enter through the ground socket and perhaps change the ground reference voltage. But it's a carbon fiber tripod! Still, I was on a quest.

    So I borrowed another 645 Pro from the store, and I took my 3 tripods up the hill. They were the Gitzo 1228, a Slik U212, and a Tiltall. All 3 tripods and both cameras exhibited this phenomenon, but to varying degrees. The Gitzo was off the most, anywhere from 1-3 stops. The other 2 did not affect the meter as much, at the most 1-2 stops. Funny thing is, the cameras did not even have to *touch* the tripod to have their readings affected! As I moved the camera closer, the meter would start overexposing by up to a stop, then jump even more once mounted.

    As a control, I then went halfway down the hill, and repeated the test. The effect was less, with the Gitzo giving 1-2 stops. I then went downtown, and tested again. No difference between on/off camera. I tested again when I got home. Again, no difference."

    What you have described could indeed be due to RF interference. Metal and carbon fiber are both conductors so the construction of the tripods may not make that much difference.

    How is it happening? This is anyone's guess but enough of a current could be induced in the sensitive electronic circuitry to throw off the meter. The ICs are full of diode junctions which can be rectifying (detecting) the relatively weak RF signal resulting in a DC offset. If this were the case and you happened to adjust the tripod height to be around 1/4 wavelength of one of the transmitters you *would* know it! :-)

    Common problems with Kodak slide projectors

    For service manuals and parts lists of newer/current model projectors, believe it or not, Kodak actually has a Web page at Kodak: Slide Projectors Family Service Manuals. (Though I don't know if they sell repair parts.) One source for some of the more common replacement parts in Kodak Equipment is Micro-Tools and search for "Kodak".

    There is also a guy selling maintenance kits on eBay. Go to the eBay search page and use search terms: "Kodak Carousel Tune Up".

    (From: Olen Burkholder (burkhood@jmu.edu).)

    I have worked on lots of these. Here is the likely problem.

    If the advance/rev buttons do not work on either the remote or the projector but the select button cycles the mechanism, the probable cause is the nylon link is broken on the change solenoid plunger. If the mechanism doesn't cycle when pressing the select button, I expect the mechanism drive belt is broken. It is separate from the fan belt. The way to tell is to look and see if the main worm gear at the motor end of the mechanism is turning when the motor is running. If it is not, the belt is the culprit.

    A note of caution. If you elect to disassemble the projector, Wrap the heat filter in a cloth. (The flat green lens in front of the lamp). If it is bare and laid on a flat surface, it can shatter spontaneously from internal thermal stresses. I know, I lost some this way. Also, Do not run the projector with the lamp burning and the case bottom removed. If you do, the thermal fuse will open within a minute or two and you will need to replace it as well (not an easy task and don't leave it out!). Also see the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

    If you have never disassembled one of these, you might want to consider whether a 20 year old projector is worth the trouble. These things can be a real bear to work on without previous experience with this design.

    (From: Johntneal (johntneal@aol.com).)

    One source for plastic gears and parts for Kodak Carousel projectors is:

    Fil's notes on Kodak Carousel repair

    In response to:

    "My IIIe slide projector does not advance the tray. When I push the switch the movement works, and I see the actuators moving (tray removed) but the tray doesn't advance. I just got this projector am I using it the wrong way or is it broken? Can someone tell me how to fix the advance mechanism."

    (From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org).)

    I would try another tray first. Then, make sure you have aligned the tray and give it another try. Try both directions. Also, put a slide all by itself into the slot and see if the mechanism works from there.

    I have fixed a few of the "Carousel custom 7xx/8xx[H]" series and they were most DEFINITELY *NOT* fun to work on. I would clean and lubricate first. Then, observe a *working* projector to see what moves where when. Timing is just about everything. At least in the 7/8xx series, there were broken plastic parts. Also, the AF gears break. I have yet to find a source for those.

    Still, I get a feeling of accomplishment getting working an AF projector after paying $7.95 at a thrift store :-) They're worth just a *bit* more. :)

    Screws hold the bottom of the case. Take them out and you should be able to lift the cover. Some of them have one slotted screw to change bulbs which also takes bottom off. Some have further assemblies that brace each-other - to take one out you have to take apart 1/2 of the projector. ARGH!

    Avoid taking it apart. If you're not familiar and don't have similar models you can study, you'll most likely end up "screwed". I got lucky. The following week found another 800H in the store for $12.95. Bad bulb socket. Clean the optics in the AF versions! >

    Slide projector autofocus

    These systems are considerably simpler than their counterparts for cameras due to the very constrained nature of the problem. In fact, as far as I know, few if any actually do any more than attempting to maintain the lens at a constant distance from the surface of the film in the slide.

    One way is to reflect a spot of light off the slide and adjust the lens so a photodetector coupled to the lens motion has that spot centered. It is really open-loop with respect to the actual focus of the lens - just maintains the position of the lens relative to the surface of the slide constant. In other words, it will maintain the wrong focus just as accurately if you don't set it properly to begin with!

    On the projectors I have seen, slides covered with glass may not work properly since there is a strong reflection from the glass itself. They assume all your slides will be of the same construction. The idea is that the film itself may bow out or in and that is what it cares about. The older ones, at least, were far from perfect.

    Where an autofocus slide projector doesn't autofocus, due to their simplicity, it should be possible to identify the faulty component. However, getting a replacement part for a 20 year old projector may be another matter. With non-use (how often do people use their slide projectors anymore?), gummed up lubrication in the motor that moves the lens or its drive train may be the most likely problem! However, there can always be bad connections and bad capacitors, photodetector, or something else. Of course, if an incandescent lamp is used to project the spot, it may just be burnt out!

    If you were to implement an autofocus system today, there would be many options including maximizing edge or even film grain sharpness with a little scanner inside the projector! The displaced spot type systems were very simple and cheap using only a few components and no fancy processors.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Motors and Relays

    Small motors in consumer electronic equipment

    A variety of motor types are found in audio and other electronic equipment. For the additional information on the specific types of motors used in VCRs and CD players, see the documents: "Notes on the Troubleshooting and Repair of Video Cassette Recorders" and "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives".

    Types of motors:

    1. Small brush-type permanent magnet (PM) DC motors similar to those found in battery operated appliances. Such motors are used in cassette decks and boomboxes, answering machines, motorized toys, CD players and CDROM drives, and VCRs. Where speed is critical, these may include an internal mechanical governor or electronic regulator. In some cases there will be an auxiliary tachometer winding for speed control feedback.

      These are usually quite reliable but can develop shorted or open windings, a dirty commutator, gummed up lubrication, or dry or worn bearings. Replacement is best but mechanical repair (lubrication, cleaning) is sometimes possible.

      Also see the section: General tape speed problems - slow, fast, or dead.

      Additional info on these types of motors can be found in "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives".

    2. A low profile or 'pancake' brushless DC motor may provide power for a in some Walkman type tape players, direct drive capstans and general power in VCRs or tape decks. Since these are electronically controlled, any non-mechanical failures are difficult to diagnose. In some cases, electronic component malfunction can be identified and remedied.

    3. AC induction motors - shaded pole or synchronous type used in inexpensive turntables. These motors are extremely reliable and are easy to disassemble, clean, and lubricate. Just do not lose any of the spacer washers on each end of the shaft and make notes to assure proper reassembly.

    4. Miniature synchronous motors used in mechanical clock drives as found in older clock radios or electric clocks powered from the AC line, appliance controllers, and refrigerator defrost timers. These assemblies include a gear train either sealed inside the motor or external to it. If the motor does not start up, it is probably due to dried gummed up lubrication. Getting inside can be a joy but it is usually possible to pop the cover and get at the rotor shaft (which is usually where the lubrication is needed). However, the tiny pinion gear may need to be removed to get at both ends of the rotor shaft and bearings.

    Motor noise in audio equipment

    Of course you expect your audio equipment to be absolutely silent unless told to perform. Motor noise should not be objectionable. However, what if it is? There are several kinds of noise: rotating noise, vibration, and electrical interference:

    If the noise is related to the rotating motor shaft, try lubricating the motor (or other suspect) bearings - a single drop of electric motor oil, sewing machine oil, or other light oil (NOT WD40 - it is not a suitable lubricant), to the bearings (at each end for the motor). This may help at least as a temporary fix. In some cases, using a slightly heavier oil will help with a worn bearing. See the section: Lubrication of electronic equipment.

    For AC motors and transformers, steel laminations or the motor's mounting may be loose resulting in a buzz or hum. Tightening a screw or two may quiet it down. Painting the laminations with varnish suitable for electrical equipment may be needed in extreme cases. Sometimes, the noise may actually be a result of a nearby metal shield or other chassis hardware that is being vibrated by the motor's magnetic field. A strategically placed shim or piece of masking tape may work wonders.

    If the noise - a buzz or whine - is actually coming from the audio output but only occurs with the motor running, the interference filter on the motor power supply may have failed. This is often just a capacitor across the motor terminals and it may be defective or there may be a bad connection.

    Finding a replacement motor

    In many cases, motors are fairly standardized and you may be able to find a generic replacement much more cheaply than the original manufacturer's part. However, the replacement must match the following:

    1. Mechanical - you must be able to mount it. In most cases, this really does mean an exact drop-in. Sometimes, a slightly longer shaft or mounting hole out of place can be tolerated. The pulley or other drive bushing, if any, must be able to be mounted on the new motor's shaft. If this is a press fit on the old motor, take extreme care so as not to damage this part when removing it (even if this means destroying the old motor in the process - it is garbage anyway).

    2. Electrical - the voltage and current ratings must be similar.

    3. Rotation direction - with conventional DC motors, this may be reversible by changing polarity of the voltage source. With AC motors, turning the stator around with respect to the rotor will reverse rotation direction. However, some motors have a fixed direction of rotation which cannot be altered.

    4. Speed - for tape players and turntables - this may not be feedback controlled. With a little care you should be able to determine the normal rpms of the motor. For example, with a cassette deck, knowing the tape speed (1-7/8" inches per second is standard), it is straightforward calculate the motor shaft speed based on simple measurements of pulley and capstan diameter ratios.

    MCM Electronics, Dalbani, and Premium Parts stock a variety of generic replacement motors for tape decks, Walkmen, boomboxes, and CD players.

    Relay basics

    The ubiquitous electromechanical relay is a device that is used in a large variety of applications to switch power as well as signals in electrical and electronic equipment. Operation is quite simple: An electromagnet powered by an AC or DC coil pulls on an armature having a set of moving contacts which make or break a connection with a set of stationary contacts.

    Most common relays can be characterized by three sets of parameters:

    1. Coil - voltage; resistance, current, or power consumption; and whether it is AC or DC. For AC coils only, the VA (volt-amps) rating may be used instead of or in addition to power consumption due to the inductive coil. Typical coil voltages range from 5 V to 480 V (AC or DC) - and beyond. Current and power consumption depend on the size of the relay.

    2. Contact configuration - number of sets of contacts and whether they are their type. The designation will be something like SPST-NO, DPDT, 4PST-NC, 6PDT, etc. The first two letters refers to the number of sets of simultaneously activated contacts (S=1, D=2, numbers are usually used for more than 2 sets of contacts). The second two letters refers to the contact configuration (ST=NO or NC but no common terminal, DT will have a common - there will be both an NO and NC terminal). Where contacts are ST, the last two letters indicate NO or NC. An almost unlimited number of variations are possible. Typical relays have anywhere from 1 to 6 or more separate sets of ST or DT contacts or a mixture of the two.

    3. Contact ratings - this may be specified for a number of types of applications. For example: in amperes at a particular voltage for DC resistive loads, or in horsepower at various voltages for AC inductive loads. Like fuse ratings, these are maximum ratings and lower values are almost always acceptable. Small relays may be able to switch only a few hundred mA at 32 V while large industrial contactors can switch 1000s of A at 1000s of V. Even the contactor in your automobile's starter must control hundreds of amps to the starter motor.

    The common (C) contacts connect to the normally closed (NC) contacts when the coil is unpowered and to the normally open (NO) contacts when the coil is powered.

    Miniature and subminiature relays are used to switch phone line signals in modems, fax machines, and telephone answering machines; audio amplifier speaker protection circuits; multiscan monitor deflection components; and many other places.

    Small relays control power in lighting equipment, TVs and other home appliances, automotive systems and accessories, and the like.

    Large relays (often called contactors) are used for the control of central air conditioning systems (compressor and blower motors), all types and sizes of industrial machinery - as well as in the starter of your automobile.

    Relay identification

    A relay without a pin connection diagram can usually be identified with a multimeter and variable power supply - or by eye. Many have the critical information printed on the cover. However, for detailed specifications, referring to the manufacturer's databook (or WEB page) really is best!

    (The following assumes a subminiature (DIP) relay. Lower coil resistances, higher coil voltages, and other variations may exist for larger relays.)

    1. If the case of the relay is transparent or you can pop the top, examine the pole piece of the electromagnet. If there is a (copper) ring around half the pole piece, the relay coil is designed for AC (usually line frequency - 50 or 60 Hz) operation. An AC relay operated on DC will overheat very quickly but can be tested on DC.

    2. Determine the coil pins. Use your eyeball if possible or your multimeter on the low resistance scale. For a small relay, the coil will most likely be a few hundred ohms. All other combinations of pins will be zero or infinity. If the resistance is under, say, 100 ohms, you may have an AC coil rather than a DC coil.

    3. Power the relay from a variable DC supply (I am assuming it has a DC coil which is likely for a DIP relay. You can still do this with an AC coil but it will heat up quickly). Start at zero and increase the voltage until you hear the contacts close. This will probably be at around 3 volts (for a 5 V coil) or 8 volts for a 12 V coil - this will be roughly 60% of nominal coil voltage. If you do not hear anything, reverse the polarity of the coil and try again - you may have a latching relay. Alternatively, put your multimeter on the resistance scale across one of the pairs of pins that measured zero ohms as it is likely to be a NC set of contacts. This will change to infinity ohms when the relay switches.

    4. Now that you can switch the relay on and off, you can use your multimeter on the resistance scale to determine which contacts are normally open (NO) and which contacts are normally closed (NC). (Normally here means unpowered.)

    5. The power rating of the contacts can be estimated by their diameter (if they are visible). Rough current estimates (resistive loads): 20 A - 5 mm, 10 A - 3 mm, 5 A - 2 mm, 1 A - 1 mm. These must be derated substantially for inductive loads.

    For latching relays, the polarity of the coil voltage determines whether the relay is switched on or off. In other words, to switch to the opposite state requires the polarity of the voltage to the coil to be reversed. Other types are possible but not very common.

    Relay testing and repair

    If the relay is totally inoperative, test for voltage to the coil. If the voltage is correct, the relay may have an open coil. If the voltage is low or zero, the coil may be shorted or the driving circuit may be defective. If the relay makes a normal switching sound but does not correctly control its output connections, the contacts may be corroded, dirty, worn, welded closed, binding, or there may be other mechanical problems.

    Remove the relay from the circuit (if possible) and measure the coil resistance. Compare your reading with the marked or specified value and/or compare with a known working relay of the same type. An open coil is obviously defective but sometimes the break is right at the terminal connections and can be repaired easily. If you can gain access by removing the cover, a visual examination will confirm this. If the resistance is too low, some of the windings are probably shorted. This will result in overheating as well as no or erratic operation. Replacement will be required.

    Relay contacts start out bright and shiny. As they are used, arcing, dirt, and wear take their toll. A sealed relay used at well below its rated current with a resistive load may work reliably for millions of cycles. However, this will be significantly reduced when switching high currents - especially with inductive loads which results in contact arcing. One speck of dirt can prevent a contact from closing so cleanliness is important. Excessive arcing can result in the contacts getting welded together as well.

    The resistance of closed contacts on a relay that is in good condition should be very low - probably below the measurable limits on a typical multimeter - a few milliohms. If you measure significant or erratic resistance for the closed contacts as the relay is switched or if very gentle tapping results in erratic resistance changes, the contacts are probably dirty, corroded, or worn. If you can get at the contacts, the use of contact cleaner first and a piece of paper pulled back and forth through the closed contacts may help. Superfine sandpaper may be used as a last resort but this is only a short term fix. The relay will most likely need to be replaced if the contacts are switching any substantial power.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Electromechanical Systems

    This chapter deals with some of the specific issues relating to the types of electromechanical systems found in items ranging from high-tech toys like the Furby(tm) - the craze a year or so ago, (see Furby Autopsy for a most interesting look into how much can be done with a little bit of technology) to more traditional low cost robots. While similar in principle, the details of high quality industrial robots are quite different are beyond the scope of this document.

    Electromechanical systems require a broad range of skills to troubleshoot because of the interaction of the software, electronics, and mechanics. While some problems like damaged mechanical parts after a mobile robot went down a flight of stairs will be obvious, others like the lack of response of a sensor could be due to many causes and a systematic approach must be taken to rule out each potential cause.

    An electromechanical system consists of: motors and actuators, sensors, mechanical components (linkages, gears, belts and pulleys, etc), controller (microprocessor, program, and data memory, and its interfaces), power drivers, and power supplies - and software or firmware.

    Motors and actuators

    Two types of motors are commonly used in small robots: DC permanent magnet (PM) motors and stepper motors:

    Sensors

    Anything that detects some physical condition can be classified as a sensor. These include:

    Detailed testing is beyond the scope of this article but the basic procedure should be to attempt to localize the fault to the sensor, interface, or elsewhere by substitution if possible since that is easiest, or measurements of the sensor inputs and outputs. For example, for an optical encoder, check that power input is correct and then look at the A and B outputs to determine if they are good solid logic levels (where appropriate) as the shaft or wheel is rotated slowly by hand. Note that in many cases, problems with erratic counts from an optical or mechanical sensor producing A/B quadrature outputs is due to incorrect software or logic - there are many ways to get it correct enough to work under continuous rotation in one direction or the other but it takes more effort (a state machine approach) to work under conditions where the shaft is jiggling back and forth.

    Testing of camera type devices can be much more complex requiring details documentation on the sensor and its electronics, a scope or logic analyzer, and a certain amount of luck!

    Controllers

    The intelligence in these systems is generally provided by a some form of programmable device. The simplest may use PICs - Programmable Interface Controllers - single chip micros with built in memory and interfaces. More capable systems may use a higher performance microprocessor or multiple processors in a distributed architecture. There is no way to cover these in this article except to emphasize the importance of recognizing that the software/firmware bugs can manifest themselves in very peculiar ways. Also, note that motors and other electromechanical actuators result in an electrically noisy environment which is shared by the controller. Unless this is taken into consideration in the design of the system, problems like random lockups or reboots or just plain unreliable operation are almost assured. More below.

    Power supplies

    Almost all of the toys and small robot type devices are (or can be) powered by some form of batteries, possibly with DC-DC converters to generate multiple voltages from a single battery pack. Weak, dead, or improperly selected batteries must be near the top of the list of common problems with these and other portable systems.

    Mechanics

    Robots almost by definition include movement. Bearings and sliding parts can become worn, gummed up, or damaged. Rule number one has to be: Never force anything. If rotation of a shaft doesn't result in the expected movement, determine why. Perhaps you're turning it in the wrong direction and it's already at one end of its travel. Or, maybe something has jammed between gears.

    Realize, however, that with many inexpensive devices like toys, everything is constructed as cheaply as possible - repair may simply not be possible if some key component has broken.

    Fortunately, if properly lubricated when constructed and operated in clean environments, additional attention may never be needed. However, water, dust, dirt, and sand can require the need for frequent cleaning and lubrication. Rule number two is: "NEVER use WD40 as a lubricant!

    Obviously, inspect for damage such as bent shafts or linkages, missing screws or cotter pins, etc.

    Troubleshooting approach

    Where a commercial product suddenly refuses to cooperate, mechanical or electrical problems are most likely. However, if you are attempting to troubleshoot a system you have built - and it uses a programmable processor - software/firmware problems must be near the top of the possibilities list, especially if it had worked before. Ask yourself: "What changed?" Has the broken function been tested since the last software change or download?

    Some items to check when dealing with robotic systems:

    Robotic and other electromechanical systems make great projects. In addition to the appear of seeing something other than electrons move and interact with its environment, the interdisciplinary nature of these devices result in an fun and rewarding educational experience, whether designing a robot from scratch, or repairing a high tech toy like a Furby(tm).



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Analog Panel Meters

    Problems with Analog Panel Meters

    While much new equipment uses digital readouts, there is still a lot of equipment out there with analog meters. And, for some applications, the continuously moving needle of an analog meter is superior to rapidly changing digits.

    The actual mechanism of an analog panel meter is most often the "D'Arsonval moving coil meter movement". Meter Movement from Classic Simpson 260 VOM shows the assembly from a very popular series of analog volt-ohm-milliammeters (VOMs) with models dating from the 1950s and still being manufactured today. A closeup with parts labeled can be found in D'Arsonval Meter Movement Anatomy. A coil of fine wire wound on an aluminum or plastic frame is mounted on precision bearings within a strong magnetic field. The needle or pointer is attached to frame along with small balance weights at each 90 degree position. Some type of restoring force keeps the needle at the zero point when no current is applied. There are two common types of bearings: jeweled bearings with hair-springs (fine spiral wire springs similar to those in mechanical clocks and watches if you remember those) and taut-band suspension (the latter becoming more common in high quality movements). In general, if no hair-springs (or their remains) are visible, the unit uses a taut-band suspension.

    With a DC current, a torque is produced which rotates the coil, frame, and needle to indicate the measured value. With a uniform magnetic field, the response is close to linear over 90 degrees. DC current is measured directly by passing it through the coil. Low resistance shunts may be used to increase the current range. DC Voltage is measured by putting a current limiting resistance in series with the meter. AC measurements are made by first rectifying the input. Where very low values are to be measured, a precision op-amp rectifier may be used.

    More information can be found at: Integrated Publishing's Pemanent Magnet Moving Coil Movement Page.

    Typical problems with these devices include:

    When all else fails, replacing the entire meter or just the movement may be the only option. Many types of analog meters are still available new from electronics distributors. Older style and/or discontinued models may be found at surplus places, particularly those catering to amateur radio. Where a suitable meter can be found but it's scale is not appropriate, a new one can be drawn or painted, or created via software. One such program can be found under "Software" at: Jim Tonne's (WB6BLD) Web Site.

    It's not impossible to rebuild a meter - just extremely difficult and time consuming. Here's a link to the Web site of someone who must have had way too much time on their hands and completely restored a TV-7 tube tester, meter and all. It's in german but the Altavista Universal Translator can do a good enough job to read it in English and it's the pictures that really matter anyhow: TV-7 Tube Tester Restoration.

    Balancing a Meter Movement

    (From: Dave M. (dgmason@att.net).)

    Pretty simple thing to do if you have deft fingers and a steady hand. If you have nervous hands, then it's dangerous to the meter for you to attempt it. It helps if you have a balance weight tool that fits the weight springs. This tool looks like a wire-wrap tool and make life much simpler with meter weights. A good, nonmagnetic tweezer with a knurled inner surface is a good alternative. If you resort to using needlenosed pliers, you risk permanent damage to the pivot and jewels. Be extremely gentle with the tool you use. And STAY AWAY from the hairspring. If you kink it or otherwise bend it out of shape, accuracy of the movement will suffer terribly.

    OK, the caveats are out of the way.

    First thing to do is to open the movement to allow easy access to the weights on the pointer. The typical D'Arsonval movement looks something like this:

          |
          |
          |
          |
          |
          |
       ---+---   <-- Side weights
          |
          |    <--  Tail weight
    

    Each arm of the pointer, except for the pointer itself, normally has a weight screwed onto it. It will look like a coil of wire wound around the pointer arm. To balance the pointer, you adjust these weights in and out so that the pointer remains in the same place regardless of the position of the meter.

    Balancing is done in two planes. First with the pointer vertical and again with the pointer horizontal. With the meter flat on the bench, adjust the meter's zero screw until it is exactly on the scale's zero marking. Next, with the pointer horizontal (and the axis also horizontal), adjust the weight on the tail (opposite the pointer) until the pointer remains in exactly the same position as when the meter is flat. Turn the meter so that the pointer is vertical. Twist the weights on the side arms so that the pointer is at exactly the same position as when the meter is flat. Repeat until the pointer remains in the same position regardless of position.

    The procedure for balancing a movement is thus:

    1. Center the front mechanical zero tang so that it is in the middle of its range.

    2. With the meter flat on its back (pivot axis vertical), adjust the rear mechanical zero tang so that the needle rests on the zero mark.

      If easy access to the rear adjustment is not possible, simply adjust the front mechanical zero tang so the needle rests on the zero mark.

      Since the pivot axis is vertical, only the mechanical (hair spring) adjustments matter.

    3. Position the meter so that the pointer is level horizontally. To clarify, this means the pivot axis is horizontal and the entire meter is oriented at about 45 degrees (on most meters) with the needle pointing to the left horizontally. Adjust the tail weight so that the pointer rests on the zero mark on the scale.

      Only the mechanical zero (performed in steps 1 and 2) and balance between the needle and tail weight matter.

    4. Position the meter so that the pointer is vertical. Adjust the side weights so that the pointer rests on the zero mark on the scale.

      (Only the mechanical zero (performed in steps 1 and 2) and balance between the two side weights matter.)

    5. Position the meter so that it sits upright on the bench (pivot axis is horizontal, pointer is at 45 degrees). If the pointer doesn't come to exactly zero scale, more adjustment is needed.

    6. Repeat steps (4) and (5) until the pointer is at zero in all positions.

    You'll find that balance will be easier if you leave the tail weight alone after the initial balance (Step 1) and use the side weights to do the final trimming adjustments. You'll have to move the side weights inward or outward in unison to maintain the vertical balance. Make the adjustments in very small increments.

    Keep in mind the principles of balancing a lever on a fulcrum; the heavier end will move down. The pointer's pivot is the fulcrum. The most difficult part of the procedure is to make the pointer balance when the instrument is upright on the bench. If the pointer is below the scale zero, then the side weights need to be moved out.

    (From: Jim Adney (jadney@vwtype3.org).)

    There are balance weights which look like little bent coil springs slipped over "spokes" which radiate out from the pivot point. These springs just have to be slipped in or out to change the balance. If, for example, the needle was shortened, you need to take the spring/weight that is 180 deg from the needle and either push it closer to center, or pull it completely off and shorten it.

    You check your work by holding the meter AXIS horizontal and then rotating it about that axis. Examine it when the needle is horizontal and again when it is vertical.

    The side-to-side balance is correct when the meter reads the same with the needle pointing straight up or down. The other axis is balanced when the meter reads the same with the needle pointing to either the left or the right.

    Once this works, the meter should also read the same as when facing up.

    Work carefully, and avoid putting any strain on the actual pivot.

    Repairing a Taut Band Suspension

    I was forced to attempt this repair after damaging the suspension in a Hastings CVT-16 thermocouple vacuum gauge controller. OK, I really didn't have to do it as replacements for the entire unit could be found relatively inexpensively on eBay but I considered it a challenge. Also, if I bought a replacement for the entire unit, I'd then have yet another set of electronics without a meter! (The meters used in these instruments are special low impedance devices so stock replacements would not work.)

    The broken meter looks like the meter portion of TC Vacuum Gauge and Pump Protector. The adjustment knob is used to move the red set-point pointer (which is mechanically and electrically independent of the meter movement itself).

    The problem occurred when I obtained a unit (not the one in the photo) that had a broken adjustment knob. In attempting to confirm that the set-point adjustment worked, I foolishly tried using a tool to turn what remained of the shaft behind the knob. Unfortunately, I didn't notice that the suspension for the front taut band is located behind the knob and unprotected. So, it basically got shredded. Can you spell "stupid design"?. :( If the knob's shaft was solid instead of hollow, there would have been no problem.

    I normally consider damage to meter movement bearings to be non-repairable but as I said, this was a challenge. :) The first step was to confirm that enough of the band remained to attach to a new suspension. After removing the front cover and set-point mechanism, the extent of the damage could be seen. The suspension was just a formed piece of metal - something springy and the band was still soldered to its twisted remains. A quick touch of a hot soldering iron and the band was free. While it was completely intact, there wasn't much of it - perhaps 1/16 inch sticking up though the "cup" where the suspension was located. And, the band is extremely thin - perhaps 1 mil x 5 mils (1 mil = 0.001 inch).

    To replace the suspension, I cut a piece of thin copper sheet into a shape that when folded over would fit in the cup. Thus, there was a top and bottom. An off-center hole was drilled and tapped for an 0-80 screw that would adjust the separation of the two "leaves". A 0.01" hole was drilled in the center of the top for the band to fit through with a larger clearance hole in the bottom. This contraption was filed so it would fit loosely in the cup.

    My original plan was to mount an XYZ micropositioner above the meter with a gripper to hold the band to enable adjustment before soldering it to the new suspension. I even fabricated a wonderful little screw clamp to use as a gripper. However, the band tip is so darn short and thin that this proved to be unworkable. So, the folded suspension almost flat was placed in the cup with the band tip poking through its hole. This affair was held down with a piece of wire fastened to a convenient screw (to prevent the surface tension of hot solder from lifting it), and the band was soldered to the suspension. Next, the 0-80 screw was installed and tightened until the meter frame/coil came free, and then some to provide clearance. The suspension was then adjusted in position to center the frame/coil and in angle to set the zero on the scale with the zero lever centered.

    This replacement is not as robust as the original since it's not very resilient. Any good whack in the direction toward the back of the meter would probably cause it to fail due to the inertia of the frame/coil but it does seem to work. Also, since the length of the free part of the band and its tension have changed, it is likely that the calibration will be slightly different.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    General Equipment

    IC and hybrid power audio amplifiers

    Note: troubleshooting of large audio amplifiers constructed with discrete output stages is left to a separate document. See: BIG Audio Power Amps.

    The audio amplifiers found in small radios, Walkmen, portable cassette recorders, and other low power devices are often single chips with few external components. Obtain a pin diagram, test inputs and output(s) with an audio signal tracer and/or oscilloscope. A dead output where inputs and power are present usually indicate a defective IC - as does one that becomes excessively hot - assuming that the output is not overloaded.

    Larger audio amplifiers may use ICs (up to 10 or 20 W) or hybrid modules (up to 100 W per channel and beyond). Purists may argue about the quality of the sound from these compared to discrete component designs but they are being used in many designs - at most price points (except perhaps the stratosphere of audiophile land).

    Hybrids modules (called 'blocks' or 'bricks' by some) may be totally self contained requiring just power and line level inputs or may be just the final stage in an overall system including external amplifier circuitry which is effectively a power op amp - high gain with negative feedback. Failure of these bricks is quite common.

    Note that testing of these op amp designs - whether discrete or brick based - can be very confusing due to the high gain and feedback. Intermediate signals in a working channel may look like power supply ripple and noise. In a dead channel these same points may appear to be normal or highly distorted audio depending on which stage you test. In addition, since extensive negative feedback is used, power supply ripple and noise is much less important significant and there may be substantial amounts of both in a normally operating amplifier.

    One of the bricks may be shorted resulting in a blown fuse or overheating of other components. It is usually safe to unsolder each of the hybrids to determine if the other channel or at least other portions of the unit come back to life and without blowing fuses.

    With stereo amplifiers, it is normally safe - and most effective - to swap components between the working and dead channels as long as you are sure there is no short circuit on the output. This is by far the quickest way to confirm a dead brick. (I would be a lot more reluctant to make this recommendation for a large audio amplifier constructed with discrete transistors in the final power stage as multiple cascade failures are possibly and likely if **all** defective parts are not located before power is reapplied.)

    Amplifier noise caused by bad hybrid bricks?

    There can be all sorts of sources for low level noise or static including bad connections almost anywhere, defective semiconductors, and erratic power amp modules. These are usually hybrid circuits - multiple devices mounted on a common substrate and interconnected via a variety of technologies. Think of them as entire subsystems encased in plastic.

    Thus, hybrid bricks may have problems with noise especially considering that they may run hot and be abused by poor tastes in music (or at least high volume levels). Thermal cycling can take its toll on this kind of device. If you have eliminated other likely causes, replacing the brick would be the next step if the module is not that expensive - how much do you value your time and hair? Of course, if there are separate bricks for each channel, one channel is most affected, and the volume control does not affect the level of the noise, the choice is clear - swap. This will be relatively low risk in most cases. A hot air gun used carefully on the final modules might also be a good way of inducing or changing symptoms resulting from marginal connections or components.

    Troubleshooting blown audio amps

    (From: Andy Cuffe (baltimora@psu.edu).)

    If it has IC's for the audio output you can just remove one of them. If the fuse still blows try removing the other one. If the fuse blows with both output ICs out you know there are problems in an other part of the unit, probably the power supply.

    If it uses transistors instead of ICs you just need to check them with an ohmmeter. The bad ones almost always measure close to 0 ohms between at least 2 of the three pins. Once you find the bad pair try the stereo with them removed. You should get normal sound from the channel with the good transistors. To determine if there is more damage to the amplifier you can swap the good transistors into the damaged channel. Before you remove anything WRITE DOWN where they go because it's easy to get them mixed up. I strongly recommend that you don't bypass the fuse unless you don't want to fix it very much. I have seen a lot of repairable electronics ruined by this type of troubleshooting.

    (From: Dakuhajda (dakuhajda@aol.com).)

    Where one channel still works, on old amplifiers we commonly remove output transistors from both channels, place a 5 watt 100 ohm resistor across the base to emitter connection of every output transistor. Then bring the power supply up on a variac and measure all the voltages on each channel. With a working channel it should be a simple matter of making DC measurements to find the area of the problem.

    (From: Wild Bill (kwag98@tcis.net).)

    A lot of the diagnosis can be accomplished with a DMM. Either the diode check test or the ohmmeter will give you a direction to proceed in. Most of these comments are related to units with through-hole (components with leads) circuit boards.. not to boards which have lots of surface mount components on the foil side.

    If you don't possess the skills, equipment and safe working habits required to perform the procedures, take the faulty equipment to someone that does. If you read the rest, you'll discover (and maybe understand) why technicians charge fees for their work.

    For almost any bipolar-transistor-output-type amplifier testing, it's a progressive process. A good starting place is checking key components for opens and shorts:

    Make notes of defective components, you can offer some help to someone else some day.

    Before proceeding to the stage of disassembly, check for circuit board mounting screws that are intended to ground the board to the metal chassis. When these get loose, this can cause a lot of weird symptoms.

    It's often necessary to start unsoldering parts since a 0.33 ohm bias resistor with a shorted transistor across it may appear to be normal. In most cases where there is no output, or the protection circuits are preventing the amp from powering up, you'll find several faulty components. Since the unit isn't powering up (or it keeps blowing fuses), you can find faults quicker (in my opinion) by checking key components without power applied. This method is also more economical since parts won't be repeatedly destroyed until eventually all of the faulty ones are replaced at once.

    Many manufacturers utilize fusible and/or flameproof small wattage resistors to prevent catastrophic damage, and all of them should be checked. They might be blue, green or tan colored.. and often have values of less than 1 ohm, but when you see this type, check all of them.

    When damaged output transistors are discovered, check the driver stage for that output.. it's often damaged too. Some driver stages use linear ICs.. if the pinout is known, compare resistance or diode check tests between all of them.

    After a thorough check of key components, and faulty devices have been replaced, remove the line fuse and replace it with a 60 watt lamp.. everyone has a well-insulated lamp with alligator clips on it, right? The lamp will usually prevent destruction of components.

    Instead of attaching speakers to the outputs (main or front L & R), use dummy load resistors. high power non-inductive (or no connections at all). The unit should be powered with an isolated variac. 40 VAC will probably be a good place to start making initial voltage measurements. You could also have an ammeter in series with the lamp, but the lamp gives a good visual indication.. brief light output followed by a barely visible glowing filament. If the lamp shows continuous light output (at this low variac setting), there is a major short somewhere near the power transformer. In that case, disconnect everything and resume ohmmeter tests. Check for components which may have gotten warm or hot.

    If a dim glow is visible, don't rush to put a fuse in and attach speakers to power it up at full line voltage yet.. but instead, start making AC (transformer outputs) and DC voltage checks (full wave bridge rectifiers, plus and minus and branch circuit supplies). Check the individual supplies DC filtering and check for the presence of AC at all of the amp's outputs with a scope.

    If all appears to be normal at reduced line volts, turn the unit off and increase the variac output to 60, make previous checks.. same for 80, 100 then 120. If dummy loads haven't been attached to the output terminals yet, turn the variac back down and repeat the previous procedure.. and check for heat at the dummy loads. With the volume control set low, there should be little heat.

    For amps with rear and center channels, check the main channel L and R first, then turn down the variac and attach dummy loads to the other channels as you repeat the previous steps.

    This seems like a lot of backing up and rechecking, but it is an economical method of accomplishing a thorough amplifier repair. Before connecting a repaired amp to the original speaker system, check the speakers and wiring.

    Audio amplifier that blows one channel's output components

    The situation is that after finding and replacing output transistors and other blown parts, the same thing happens again almost immediately or sooner.

    (From: Mike Ross (mike.ross@juxta.mnet.pubnix.ten).)

    Before you blow up any more parts insert some temporary current limiting resistors (i.e. 330 ohms 10W is okay) in series with each individual output transistor collector lead. If the transistors saturate then there is either a bias idle current or still yet an offset voltage problem.

    Blown diodes and resistors in the bias voltage reference circuit could easily cause the outputs to self destruct. One common design problem is seen with the adjustment trimmer pot, in that if the wiper opens then it results in maximum idle current. Of course they should always be designed so that if the wiper opens then the idle current goes to minimum. This could be one cause. Good luck.

    If all else fails, hurl it across the room a few times! :)

    (From: Dave (gravman@idirect.com).)

    Where one channel blows outputs, check the zobel network components. This is a capacitor (usually green mylar with values of .047 to .1 uF) connected in series with a low ohm resistor (2.7 to 8.2 ohm) BETWEEN the speaker line and common ground. I have seen a few amps with the same symptom and the cause was that capacitor blown OPEN! Cranking up the treble full at very high volume levels can cause this to occur. Even a nearby CB or HAM transmitter with lots of watts can inject into your unshielded speaker leads and blow that cap!

    When that cap goes open circuit, the amp will oscillate at a high frequency beyond hearing range. I've scoped as high as 80 KHZ!

    If those two components are OK, and you have definitely confirmed that all others are OK, leave the output transistors out, install a 100 ohm 5W speaker load resistor and power up the amp with a DC voltmeter in place. You should measure much less than +/- .6 volts DC across that dummy load. If the voltage is more, you've got a improperly installed transistor, bad bias pot, defective front end differential pair transistor(s), leaky/damaged bias diodes, etc. Check, double check, and re-check your components.

    If the voltage is within proper range, connect a scope across the dummy load resistor, slowly increase input music or sine-wave. If you see a extremely blurred signal, shut down the amp and search for possible defective small pF value compensation capacitors in other parts of the circuit. You may have to pull each one and check/replace until you find the culprit. You may simply have a leaky/flaky transistor in there somewhere. You may also have a corroded/loose ground connection or bad solder joints too!

    Do these tests, and see what you find. ALWAYS CHECK YOUR OWN WORK THREE TIMES BEFORE CURSING!!!

    Audio amplifier that seems to have reduced power

    (From: Jerry Greenberg (jerryg50@hotmail.com).)

    The first step is to verify the voltages in the power supply for both the preamp and output stages.

    I would also start by changing the main filter caps in the power supply to start. This is the only true way to test these...

    The best way to test for such a problem is to feed an audio generator into the amp and put an 8 ohm dummy load for the speakers. Use a scope and go through it to see what is happening. Set the audio generator to a 40 or 50 Hz tone.

    The test for the output stage is to turn up the volume with the scope across the dummy load to start. See and measure the amplitude of the waveform to determine the voltage P-P output. You should see where it is starting to distort the waveform, and back off about 5 to 10%. From that calculate the RMS, and then calculate the actual Power. If it is more than than the rated output of the amp you are overdriving it anyways...

    Don't leave high volume tone into the dummy load for more than a few minutes at at time. This is hard on the unit for long periods of time...

    Note* I have found many consumer amplifiers can only put out their rated power at 1kHz. Only the high quality ones can do it at all frequencies... At about 50 to 80 Hz most consumer amps will only put out about 50 to 70% of their rated power...

    Comments on recurring audio amplifier failures

    (From: Mark Kinsler (kinsler@adenine.frognet.net).)

    The classic failure of output transistors in audio equipment is the collector-emitter short, which is typically caused by overcurrent, which is typically caused by someone short-circuiting the speaker wires together in an attempt to add or move the speakers, which is typically caused by someone being at a party and drunk.

    (From: Tom MacIntyre)

    Whenever someone brings an amp in for what looks like blown outputs, we try to talk them into bringing the speaker cables in, so the ends can be tinned properly. No extra charge, and maybe save them a few bucks from a few strands doing the short-circuit thing.

    The only way to prevent a recurrence of the problem is to install fast-blow fuses in series with the speaker lines deep inside the receiver where the owner cannot find them.

    They'll find them if they want to, but your point is well-taken.

    (From: Phillip R. Cline (pcline@iquest.net).)

    I used to work on high end audio stuff and when properly designed an amp can take a direct short at full power or any other level the volume may be set. Having said this I must qualify my statement. I did say I worked on high end stuff. This would not include the systems that appear to be a rack or component system but is in fact one big front panel molded to look like a group of individual components stacked on each other. This also doesn't include the vast majority of Japanese mid-fi stuff made and sold since about 1980 to the present. Most of that stuff use DC coupled amps and no speaker protection circuits or they use the infamous STK or SVI series of hybrid amp modules. These tend to be very unreliable and the output stages fail in these on a regular basis. Another problem is that often times there is now where near enough heat sink on the output devices and they overheat and fail. On one JVC amp that would be considered high end the engineers in their infinite wisdom decided to power one half of the bipolar supply going to the preamp op-amps through a panel lamp on the front panel. Guess what happens when the lamp opens up? Catastrophic failure of nearly all the semiconductors occurred when the lamp burnt out. This caused the speaker protection circuit to be effectively disabled and all the main power supply current fried everything including the woofers in the speakers due to a severe offset voltage present due to the lamp failure removing one side of the bipolar supply of the preamp section. Nice work on the engineers part.

    When we got an amp with suspicious failure mode we always wanted to see the speakers to make sure that the owner didn't crank the amp up until it was clipping which would in some cases fry the crossover caps as well as the tweeters and mids and in more severe cases the woofers also thus rendering the speaker a very low value resistor which would in turn fry the amp. To prevent this we would sometimes have to increase the crossover caps voltage rating and we might even through a fuse in the speaker cabinet somewhere. That way when the fuse blew the customer had no choice but to tell the reason for the failure after being confronted with the evidence.

    This kind of stuff is the primary reason for me leaving the repair business after the fact that most consumer audio and video stuff except TVs are made disposable.

    Substituting Darlington transistors in audio amplifiers

    (From Daan van der Veer (D.J.C.vanderVeer@stm.tudelft.nl).)

    I have good experiences with the use of Darlingtons instead of normal output transistors in audio power amplifiers. The only problem is that you have to readjust the bias current of the bases of the drivers. Furthermore, reduced or increased frequency response is almost always corrected by the amplifier's feedback.

    Readjusting the bias current is very simple with a scope and a sine wave generator, but could also be done with a simple voltmeter. And a computer is a very handy tool in diagnosing amps, if you have a soundcard, you can (mis)use it to measure a frequency response of any everyday amp (frequency response of most soundblaster compatible soundcards is 44 kHz). And with a very precisely tuned high quality notch filter you can even measure the THD of any amp, *real-time*. (This is very handy if you want to adjust output transistor bias current, to a minimum of crossover distortion).

    Comments on power supply regulation in audio amps

    (From: DangerDave (dangerdav@earthlink.net).)

    I can't speak for all audio designers, but here are a few things I consider:

    1. Differential output stages cancel in-phase sag/ripple

    2. Regulation can add noise

    3. Regulation adds complexity/reliability problems

    4. Regulation adds cost

    5. Other things are often more important than regulation to a predetermined voltage - e.g.; sag, ripple, stiffness, Zout. Letting the power supply DC output go as the mains voltage is usually good to within 5% or so, thus absolute regulation to a set-point voltage doesn't buy you much power headroom, and does create the possibility series regulators will overheat if the mains voltage rises. If the output stage is high power, the PS must supply high current, thus the overheating concerns under conditions of high mains voltage.

    6. A little more complex argument - distortion products are determined by the order of the transfer functions of the subcircuits. The lower the order of transfer function, the lower the order of distortion artifacts. Under NFB conditions, the situation is more complex, as phase, gain, and bandwidth constraints interact with the PS's transfer function, to create multiplicative artifacts, leading to IM, TIM, and other spectral artifacts. You can easily create "loop within a loop" problems using servo'd voltage regulation. This topic really deserves more discussion. IIRC, Norman Crowhurst originally worked out multiplicative distortion mechanisms graphically in the 1950s and published them in Audio. Since that time TIM and other spectral distortion mechanisms have been further analyzed in AES and IEEE.

      Basically, a simple, low order PS transfer function may create fewer and lower order multiplicative artifacts (less objectionable distortion). The main thing is to keep the PS high in equivalent capacitance and low in Zout - e.g., an "ideal" voltage source. You don't need set-point regulation to accomplish this, and elimination of closed loop feedback voltage regulation usually makes the PS's transfer function lower order.

      The simplest way to do this is giant caps in the PS. This is a popular approach among high end audio companies at this time. Some advertise "X uF of Capacitance" or "X Joules of Energy" A better approach is to use the new generation FET's, IGBT's, and other extremely low series resistance pass elements. Referenced to a stable voltage, the equivalent series output resistance of PS's so designed can be < 1 ohm, 20-20kHz, and no need to fill the box with giant (and expensive) caps. Reduces in-rush problems as well, so you don't add complexity/reliability problems with controlled ramp-up circuits, timed power-up schemes, and the host of ancillary circuitry required to keep breakers from triping. :) Equivalent transfer function and parts complexity can both be low, relative to servo'd NFB voltage regulation schemes.

    Big topic. Interesting question. Hope I gave you a few insights.

    Noisy or intermittent switches and controls

    Symptoms include audible noise when rotating knobs, erratic operation of mode selectors, random changes in volume, switches, or controls that need to be jiggled or tapped to make them cooperate.

    The causes are likely to be either dirt or wear.

    First, try a spray control/contact cleaner - even the stuff from Radio Shack may make a remarkable difference iff (1) dirt is the problem and (2) you can get the cleaner inside the troublesome part.

    DO NOT use WD40 or a similar product because aside from the flammability issues their use may result in rapid failure even if you get the immediate gratification often provided by these sprays. See the section: Why NOT to use WD40 on noisy controls.

    Some types of contact and control cleaners can be used safely with low voltage circuits while they are powered but not always - read the label directions. Select a product that specifically states that is it safe for switches and controls.

    Use the extension tube that comes with the spray can and snake it into or near any visible access holes. Operate the control or switch to help the cleaning action. Don't overdoe it - if you get to the right spot, a little is all that is needed.

    Resist the urge to use sandpaper or steelwool (ack!) on switch or connector contacts. However, pulling a piece paper through a set of contacts or the occasional gentle use of a soft pencil eraser (e.g., Pink Pearl) may be helpful.

    If this does not help - or only helps short term - the part may be worn. Sometimes, repair is possible (a slide switch with contacts that have loosened with use, for example) but replacement is better - if you can find an exact or suitably close match. See the section: Interchangeability of components.

    Note that capacitor type frequency select controls may also be subject to noise as they are rotated. This may also be due to dirt/oxidation between the rotating part and the stationary connector. Some contact cleaner should help. For large variable capacitors with air between the plates, there may also be conductive slivers or dust that has found their way in between the plates - use a brush to remove these. Some plates may also have gotten bent somehow (e.g., if you were doing some other work in the area).

    Why NOT to use WD40 on noisy controls

    This may not apply to the resistive elements in all/many/most controls but why risk it?:

    (From: Richardson (rchvid7@flash.net).)

    Here are some facts after seeing the results first hand in an environment where Pro TV editors were using up controls in audio mixers manufactured by Shure Brothers. WD40 when used for the first time resulted in good operation for 5 days. After that time the controls started to deteriorate very quickly and were junk the next week.

    The situation was clear after opening up the pots afterward. The carbon material was bonded to itself and to the phenol substrate by some chemical which became soft after being exposed to the hydrocarbon base of the WD40. It soon deteriorated to mush.

    The use of LPS 1 did not cause such a dramatic failure of the surfaces but did not provide any improvement that lasted.

    In the past we could get good results with Freon cleaning spray, but it is getting harder to get than the replacement controls.

    In test pots the only way to get an improvement was to carefully remove residue and relubricate with a lubricant like Radio Shack "Gel Lube" or the latest Sony grease available for broadcast and pro use.

    Resuscitating potentiometers

    (From: Rene Zuidema (cps_rjz@cistron.nl).)

    Often, pots are not really dirty, but the pot wiper just worn out the resistive layer. No amount of cleaning will solve the problem.

    Just carefully re-bend the wiper contacts to follow another track alongside the damaged resistive material. If done well, the wiper will now track intact resistive material again. As new!

    This specially works for servo's as used in RC cars / planes etc. In these applications the resistive track around the servo neutral position is worn out after some seasons of use.

    (From: Paul Weber (webpa@aol.com).)

    Disassemble the pot by carefully bending the tabs that hold the cover on (assuming this is a cheap consumer type pot). Inspect the works with a magnifying glass; find the fingers on the rotor that touch the resistor material. Using a needle or dental pick carefully bend the fingers out of the furrow they've worn in the resistor material. Objective is to make contact with an unworn area on the resistor material. Clean the whole thing with spray cleaner and re-assemble.

    Overall resistance may be slightly changed due to the lost resistance material, but this is usually not a problem in consumer applications. Good luck!

    General intermittent or erratic behavior

    Any intermittent problems that cause random sudden changes in performance are likely due to bad connections, internal connectors that need to be cleaned and reseated, or dirty switches and controls. First, see the section: Noisy or intermittent switches and controls.

    Bad solder joints are very common in consumer electronic equipment due both to poor quality manufacturing where cost reduction may be the most important consideration. In addition solder connections deteriorate after numerous thermal cycles, vibration, and physical abuse. Circuit board connections to large hot parts or parts that may have mechanical stress applied to them are most likely be suffer from hairline solder fractures (often called 'cold solder joints' when they result from poor quality soldering at the time of manufacture). However, since the solder is often the only thing anchoring these components, mechanical stress can eventually crack the solder bond as well.

    To locate cold solder joints, use a strong light and magnifier and examine the pins of large components and components that are subject to physical stress (like headphone jacks and power connectors) for hairline cracks in the solder around the pin. Gently wiggle the component if possible (with the power off). Any detectable movement at the joint indicates a problem. A just perceptible hairline crack around the pin is also an indication of a defective solder connection. With the power on, gently prod the circuit board and suspect components with an insulated tool to see if the problem can be effected.

    When in doubt, resolder any suspicious connections. Some device may use double sided circuit boards which do not have plated through holes. In these cases, solder both top and bottom to be sure that the connections are solid. Use a large enough soldering iron to assure that your solder connection is solid. Put a bit of new solder with flux on every connection you touch up even if there was plenty of solder there before.

    In addition to soldering problems, check for loose or corroded screw type ground (or other) terminals, and internal connectors that need to be cleaned and reseated.

    Need to turn up volume to get sound to come on

    If at times, it is necessary to turn the volume way up or possibly to tap or whack the unit to get the sound in one or both channels to come on when the unit is first powered up, the speaker protection relay could be faulty. Receivers and audio amplifiers often include a set of relay contacts in series with each output to protect the loudspeakers from power-on and power-off transients as well as damage due to a fault in the audio circuits. However, these contacts may deteriorate after awhile resulting in intermittent sound.

    While this set of symptoms could be the result of general bad connections or even dirty controls or switches, the relay is often at fault. This is exacerbated by switching the unit on and off at high volume levels as well as this may cause contact arcing.

    To determine if the relay is at fault, either test it as outlined in the section: Relay testing and repair or with the unit on, very gently tap the relay to see if the sound comes as goes. If the relay is bad, you can try cleaning its contacts or replace with one that has similar electrical specifications as long as you can mount is somehow. Don't be tempted to bypass the relay as it serves a very important protective function for both the amplifier and your loudspeakers.

    If it is not the relay, see the sections: "General intermittent or erratic behavior" as well as "Noisy or intermittent switches and controls".

    Speakers take a while to come on

    You turn on your stereo receiver and everything appears normal - display, tuning, signal strength, etc., but there is no sound. A few minutes later, just when you had entirely given up any hope, there is a click and everything is normal - until the next time you power down. The amplifier is taunting you - hehe, I will come on when I feel like it!

    (Note that if it never comes on, then there could be a real problem that the protection circuitry is catching such as shorted components in one of the power amplifiers.)

    This sounds like the signal to power the speaker relays is not being generated. The underlying cause could be a fault in the time delay or fault protection (overload) circuit.

    It could be as simple as a bad capacitor. A first test might be to check for an audio signal at the input to the speaker relay. If there is signal almost as soon as you power it up, then trace back from the relay coil to see what type of circuitry is there. A schematic will probably be needed unless you find an obvious bad connection or dried up capacitor.

    Amplifier clicking and shutting down on music peaks

    (From: Frank Fendley (frank.fendley@datacom.iglou.com).)

    It sounds like the protection circuit (usually a relay) is cutting in during louder music passages. This is caused by an imbalance in the amplifier circuitry, generally resulting in a DC offset voltage appearing on the output. The usual cause is a defective transistor(s), probably in the earlier stages in this case.

    Of course, it could also be that you have 10 sets of speakers connected to the amplifier and all the volume levels turned to the stops - it is simply protecting itself from abuse! :-) --- sam.

    Speaker outputs do not come on or shut off immediately

    (From: Ronald Dozier (dozier@strauss2.udel.edu).)

    The protection relay usually detects DC offset at the speaker terminals and then open's the speaker leads. Check for a DC offset > 100 mV or so before at the output, before the protection relays.

    Leaky outputs are the first to suspect.

    In most PP drivers the voltage between the bases of the output transistors should be about 2 Vbe or around 1.2 volts. 0V is definitely a problem. I have only seen one amp (mine) that used 4 Vbe. or about 3.2 volts. The voltage across the emitter resistors without a load are in the 0 to 20 mV range. This voltage should not increase appreciably over time and is set with the bias adjustment. Careless playing with the bias pot will result in output transistor destruction. It is best set with the aid of a distortion analyzer.

    All resistors/transistors in the driver and output stage and in some cases the pre-amp are all suspect. The small valued ones like to change value. Compare with functioning channel.

    Speaker thump - $2,000 amps versus PCs

    (From: (filipg@repairfaq.org).)

    Your stereo doesn't do this because it has a relay that doesn't turn on the speakers to the amp until AFTER it "thumps"! So, even a $2000 amp "thumps" it's just that there is a *provision* for that in the design. Altec has to compete with crappy brands that offer "200W" for $9.95... they can't afford to put in a $0.55 relay (*2 million units, you do the math for their total cost).

    The reason they use the relay on the "speaker" side and not the "volume" side is so they can also have a "speaker protection" in the same deal - if you exceed some volume for too long, the relay will disengage the speakers, preventing their demise. You have not such worries so I suggest a small relay in the volume side of the speaker.

    A 555 timer set for ~1 second will do nicely. Power it off the amp's power and set it to energize the relay after 1 second. The "thump" will still happen, but the volume will be "0". Put the relay in line with the wires to the volume control such that when it is not energized (i.e., amp off) it sets the volume at 0 and when energized (1 second after amp on) the pot controls the volume.

    Problem solved.

    BTW, your amp isn't technically "broken" - it's just designed that way. :-)

    Determining power output of amplifier

    You need a load resistor of a value equal to the ohms rating of the speakers you intend to use and a power rating sufficient to handle the maximum you expect the amp to put out for a short time at least. Then, all you need to do is drive it until just below clipping and measure the voltage. P=V^2/R. This really requires an audio signal generator but some music with a sustained high level might be sufficient to make measurements. Of course, unless you have an oscilloscope, you will have a hard time determining when clipping occurs without destroying a set of speakers in the process. :(

    Strictly speaking, you need to do this simultaneously on both (all) channels as a weak power supply can also limit power output but that is for the advanced course!

    Dead channels on front-end audio components

    Unlike big amplifiers, these are not normally failures caused by abuse or high power components. This type of equipment includes preamps, cassette decks, CD players, tuners, etc.

    First, eliminate the audio patch cables by trying a different set or swapping left and right at both ends. In addition, confirm that your amplifier is operating on all cylinders (or channels).

    Assuming this does not turn up anything:

    For a tuner, the problem is almost certainly very near the output - probably a bad connection, bad jack, or bad final IC or transistor stage. There isn't much between the demodulator and the line output.

    For a tape deck, much more can be involved. First, clean any mechanical REC/PLAY mode and other switches with contact cleaner as dirty contacts may result in one channel dropping out. If this does not help, determine if the output of the tape head is making it to the toutput by touching the terminals on the playback head with a tiny screwdriver when in play mode - you should get a hum when you are on the appropriate signal wire. If there is none for the bad channel, then you will have to either trace forward from the head or backward from the output. If you do hear a hum in the defective channel, the tape head itself may be bad - shorted or open - very dirty.

    Older tuners, receivers, premaps, tape decks, etc. used discrete transistors and circuit tracing was possible. Modern equipment relies on ICs but pinouts, at least, are generally available by checking a cross reference guide such as those put out by ECG, NTE, or SK.

    Again, first eliminate bad jacks or cables -- and with tape decks - clean the REC/PLAY (and other) mode selector switches.

    Repairing stereo headphone plugs/cables

    This is only worth the time, effort, and expense if the original cost was substantial. It hardly makes sense to pay $2 for a replacement plug and an hour of labor to repair a Dollar Store set of headphones!

    The most common location for broken wires is at the plug end due to repeated stress. Sometimes these can be repaired by pealing back the rubber boot, cutting, stripping, and soldering the broken wires end-to-end. However, in most cases, you will grow old attempting to do this successfully and replacing the plug is the desirable solution. Radio Shack or any real electronics distributor will have the required "1/8 inch stereo phone plug". If you don't want to solder, they are available with teeny tiny screw terminals.

    Note: Sometimes the wires break at other locations so replacing the plug may not help!

    There are a pair of shielded wires which need to be cut back to well beyond where the break took place (to expose undamaged wire), stripped carefully to expose the inner conductor and separate the outer braid/shield. This wire is really really thin and fragile so if you have trouble opening a zip-lock bag, leave the repairs to someone else. :)

    
          ----._________ ____ __
               _________ ____ __>
          ----'
                 Collar  Ring Tip
                  Gnd   Right Left
    
    

    Equipment hums or buzzes

    Assuming there are no other symptoms and the sound is coming from inside the unit and not the loudspeakers, this is probably simply due to vibrating laminations in the power transformer or motor(s) or nearby sheetmetal that is affected by the magnetic fields from the power transformer or motor(s). Most of the time, this is harmless but can definitely be quite annoying especially when one expects total silence from their audio equipment. If the noise is coming from any motors or their vicinity, refer to the section: Motor noise in audio equipment.

    Sometimes, simply tightening the screws that hold the transformer or motor together or the mounting screws will be all that is needed. Placing a toothpick or piece of plastic in a strategic location may help. It is also possible to coat the offending component with a varnish or sealer suitable for electronic equipment but be careful not to use so much that cooling is compromised or getting any in bearings or locations that would interfere with rotating parts.

    Dirty power - a light dimmer on the same circuit - may also result in increased magnetic noise. See the section: Dirty power and buzz from equipment.

    If the hum or buzz is in the audio, there could be a bad filter capacitor in the power supply, other power supply problems, bad grounds inside the unit or general ground problems with external equipment, or other bad connections. Disconnect all external devices (except the speakers if you do not have a pair of headphones) and determine if the problem still exists. Proceed accordingly. Some Sony receivers are known to develop bad grounds internally and just tightening the circuit board mounting screws and/or resoldering ground connections will cure these.

    Overloads can also cause a hum or buzz but would generally result in other symptoms like a totally or partially dead amplifier, severe distortion, smoke, six foot flames, etc.

    If the problem is only annoying when the equipment is not in use, as a last resort (where no memory or clock functions run off the AC line), putting in an AC line switch may not be such a bad idea.

    Dirty power and buzz from equipment

    Power line waveforms that are not sinusoidal can cause buzz. Multiple devices on the same circuit (or even different circuits) can interact. A TV or other equipment may add to the problem since its switching power supply draws current only on part of each cycle.

    Excessive voltage can also increase the 'magnetic noise' from motors and power transformers. This sound is a result of core or winding vibrations.

    You need to check for both of these possibilities - a calibrated scope is best. DMMs and VOMs may not read correctly with non-sinusoidal waveforms.

    Will line voltage fluctuations affect A/V equipment

    When large applicances like air conditioners, refrigerators, and heaters kick in, there is often a momentary dip in line voltage (especially if they are on the same branch circuit) which is very visible on incandescent lamps but is it actually harmful to electronic equipment?

    It really depends on many factors but a couple percent variation in voltage (which is probably what you are seeing) probably isn't going to affect your A/V equipment in any way. Most modern equipment includes internal voltage regulation so there could indeed be no detectable effects.

    Note that the volt or two drop in the wiring isn't in itself dangerous since it is distributed over a large length of wire. For example, a 2 V drop with a 10 A load is only 20 W lost in the wiring which over 50 or 100 feet is negligible heating. However, if this just started happening with no changes or additions to the wiring - especially if it is erratic - it could be due to a bad connection which is potentially dangerous and should be checked out.

    A line filter might be of some value if you are actually seeing or hearing interference when the offending equipment kicks in. However, if you can't detect it, don't worry about.

    Note that a surge suppressor is basically useless for this sort of voltage fluctuation as it only kicks in with a very significant *increase* in voltage.

    WARNING: If you are actually seeing your lights *brighten* when that equipment starts up, get your electric wiring checked out. This could indicate a loose Neutral connection and that can result in expensive damage to anything plugged into your residence's electrical system and a safety and fire hazard. See the document: Notes on the Troubleshooting and Repair of Small Appliances and Power Tools for more information on this and other wiring problems.

    Identifying and correcting sources of interference

    Although this is a rather special application, similar problems and solutions apply to other interference problems. Also see the section: Interference on AM radio band.

    "I am using a 12V DC to 110 VAC converter in my car, to run a small TV/VCR. It works fine. But the TV speaker is not very good.

    So I got one of those cassette adapters that has an audio cassette on one end, and a headphone jack on the other. I plug that into the TV, and the cassette slot on my car stereo. So then I can hear the TV sound on the car speakers, which are much better speakers.

    But now there is a lot of high frequency noise that way, on the car speakers. It is very irritating. A high frequency buzz of some kind. How can I reduce or eliminate that noise?"

    (From Duncan (duncan@punk.net).)

    First we have to figure out where it is coming from. The inverter is certainly a noise source, and without spending a large sum for a well filtered inverter you have to deal with the noise somehow.

    One possibility is that the noise is on the 12 volt power supply going to your car stereo. To test for this, play a blank tape while running the TV and listen for the same noise. Fix with filters on the power leads of stereo and/or inverter, wire to a solid clean rail very close to the battery.

    Another possibility is capacitive coupling between the TV, connected to the higher voltage side of your inverter, and the tape deck's playback heads. This might be alleviated by using a different, more isolated inverter or by using another method of getting the audio into the stereo system. FM modulators intended for portable CD players might work.

    Another possibility is that the power supply of the television is not rejecting the higher frequency components of the inverter's signal. The fix here would be to add more capacitors and perhaps resistive or inductive filter elements inside the television. Check this by plugging headphones into the same jack and listening for the noise.

    Still another possibility is that the noise you hear is part of the horizontal sync signal, which is not rejected well by all televisions. This causes a high pitched continuous squeal which is inaudible to some people. The only easy work-arounds here would be to try a different television or to turn down the treble or select Dolby-B on your car stereo. To test for this effect, try the same hookup in your house with your home stereo, cassette deck, adaptor cassette, and television.

    Or just hook up your HiFi stereo VCR to the home stereo, move the whole mess into the car, and ignore the car stereo. Four of Radio Shack's little Pro-7 speakers with a Marantz 25 watt by four channel amplifier worked quite well for me, especially when combined with a hand-held LCD monitor :-).

    Interference on AM radio band

    This sort of problem is usually in the form of a buzz or hum at 60 Hz or 120 Hz (or 50 Hz or 100 Hz if your power is at 50 Hz). There may be a little of this on a small portion of the AM band but if it is excessive and interferes with even strong stations, then a remedy is needed! The following approach should serve to locate the source if it isn't obvious:

    (From: Doug (dslosty@pipeline.com).)

    First, turn off the main house breakers and listen on AM with a battery operated portable radio.

    If the noise has disappeared, then you are generating the interference in your own home and its time to check out things like light dimmers, fluorescent lamps, touch-control incandescent lamps, motors, even cordless phones, etc.

    If the interference is still present on the portable AM radio, with the breakers off, walk around the perimeter of the house and see if it's loudest near the electric service entrance.

    If it is, walk up and down the street and try to see if the intensity varies (your neighbors will think you're weird - but what the heck!).

    If the interference comes from outside of your home, it's time to call the electric utility company and ask to speak with one of their engineers. The electric industry is required by the U.S. FCC. to keep radio interference (RFI) to a minimum. They may try to stonewall you but if you persist, they will sent out an engineer with radio direction finding equipment to locate the source of the interference. If the source is a piece of equipment on a non-cooperative neighbor's property, you may have another problem - but - one step at a time.

    I've been through this procedure several times. Last time, the electric company engineer tracked it to a broken and arching pole insulator.

    As a former AM broadcast engineer (and current HAM radio operator), I've experienced this problem enough to know that while challenging, the interference source can always be found.

    (From: Mr Fixit (mrfixit@cyberhighway.net).)

    Radio Shack sells RF chokes. Label says "SNAP-ON FILTER CHOKES (2) cat. no. 273-104"

    They open up and snap together over your wires. Very simple to install and come with comprehensive instructions.

    With a little experimentation you can see if you need it on your power cord, on the speaker wires or both. (these wires can act as antennas for certain frequencies of RFI)

    I use them all over my house on phones, TV's, stereos, computer speakers etc to block out RFI from my CB base station and vis-versa.

    BTW: if you happen to have any unneeded computer monitor cables laying around, the oversize collar near the end is a RF choke. I had a couple so I cut the covering and slid them off the cable. I put them onto our cordless phone base unit antenna as an experiment to see if it would reduce the ever-present buzz it had. To my surprise, the buzz disappeared with no loss of signal strength.

    (From: Dan Hicks (danhicks@millcomm.com).)

    An even better idea is to put these chokes on the RF **generators** in your house. I'm not sure if it's "code" to install them on permanent wiring, but it should be safe to do so so long as you are reasonably careful. And it's easy to install them on any plug-in devices that appear to cause problems.

    Internal fuse blew during lightning storm (or elephant hit power pole)

    Power surges or nearby lightning strikes can destroy electronic equipment. However, most of the time, damage is minimal or at least easily repaired. With a direct hit, you may not recognize what is left of it!

    Ideally, electronic equipment should be unplugged (both AC line and phone line!) during electrical storms if possible. Modern TVs, VCRs, microwave ovens, and even stereo equipment is particularly susceptible to lightning and surge damage because some parts of the circuitry are always alive and therefore have a connection to the AC line. Telephones, modems, and fax machine are directly connected to the phone lines. Better designs include filtering and surge suppression components built in. With a near-miss, the only thing that may happen is for the internal fuse to blow or for the microcontroller to go bonkers and just require power cycling. (Unplug the unit from the wall for a couple minutes and see if that will reset it.) There is no possible protection against a direct strike. However, devices with power switches that totally break the line connection are more robust since it takes much more voltage to jump the gap in the switch than to fry electronic parts. Monitors and TVs may also have their CRTs magnetized due to the electromagnetic fields associated with a lightning strike - similar but on a smaller scale to the EMP of a nuclear detonation.

    Was the unit operating or on standby at the time? If was switched off using an actual power switch (not a logic pushbutton), then either a component in front of the switch has blown, the surge was enough to jump the gap between the switch contacts, or it was just a coincidence (yeh, right).

    If it was operating or on standby or has no actual power switch, then a number of parts could be fried.

    Many devices have their own internal surge protection devices like MOVs (Metal Oxide Varistors) after the fuse. So it is possible that all that is wrong is that the line fuse has blown. Remove the case (unplug it!) and start at the line connector. If you find a blown fuse, remove it and measure across the in-board side of fuse holder and the other (should be the neutral) side of the line. With the power switch off, this reading should be very high. With the switch on, it may be quite low if the unit uses a large power transformer (a few ohms or less). For example (assuming power transformer operated supply):

    Some may be outside these ranges but if the reading is extremely low, the power transformer could have a partially or totally shorted primary. If it is very high (greater than 1 K ohms), then the primary of the power transformer may be open or there may be blown thermal fuse under the outer insulation wrappings of the transformer windings. This may be replaceable but don't just bypass it (except for testing). See the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

    If the unit has a switching power supply (the AC input doesn't go to a power transformer but gets rectified and filtered first), see the document: Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies.

    If the resistance checks out, replace the fuse and try powering the unit. There will be 3 possibilities:

    1. It will work fine, problem solved.

    2. It will immediately blow the fuse. This means there is at least one component shorted - possibilities include an MOV, line filter capacitor, transformer primary.

    3. It will not work properly or still appear dead. This could mean there are blown fuses or fusable resistors or other defective parts in the power supply or other circuitry. In this case further testing will be needed and at some point you may require the schematic.

    Use of surge suppressors and line filters

    Should you always use a surge suppressor outlet strip or line circuit? Sure, it shouldn't hurt. Just don't depend on these to provide protection under all circumstances. Some are better than others and the marketing blurb is at best of little help in making an informed selection. Product literature - unless it is backed up by testing from a reputable lab - is usually pretty useless and often confusing.

    Line filters can also be useful if power in you area is noisy or prone to spikes or dips.

    However, keep in mind that most well designed electronic equipment already includes both surge suppressors like MOVs as well as L-C line filters. More is not necessarily better but may move the point of failure to a readily accessible outlet strip rather than the innards of your equipment if damage occurs.

    It is still best to unplug everything if the air raid sirens go off or you see an elephant wearing thick glasses running through the neighborhood (or an impending lightning storm).

    Surge Suppressor/UPS cascading

    (From: Fred Noble (f-noble@suttondesigns.com).)

    A large number of users still seem confused about the use of a Surge Suppressor in line with a UPS. The general rule is, do NOT plug a surge suppressor INTO the OUTPUT of a UPS that produces a non-sinewave output that exceeds 5% Total Harmonic Distortion (or THD) when the UPS operates from battery supporting any load under any ambient conditions. Do NOT plug a Line Conditioner or other type of filter into the UPS either.

    You can plug a UPS into a well grounded surge suppressor, but this is not always a good idea, especially when we are talking about various 'low cost' surge suppressors of questionable electrical integrity. We constantly hear of low-end surge suppressor recalls for safety reasons, with several recent recalls ordered by the U.S. Consumer Product Safety Commission, for example, http://cpsc.gov/cpscpub/prerel/prhtml97/97078.html. A cursory search using the keywords 'surge arrester consumer recalls' with the Excite engine reveals several such recalls.

    If the surge suppressor you plug the UPS *into* is electrically 'safe' you are still extending the ground path with such a cascading arrangement, which, on balance, may not be wise. The UPS should provide Surge Suppression energy ratings of 480 Joules or more. Then, you probably wouldn't require the additional upstream surge suppressor at all. This does not mean that you shouldn't also have a surge suppressor installed at the MAINS or the branch panel, however. We are only talking about the extra, stand-alone, AC protection devices.

    This is also not to say that you should not provide additional surge suppression for your modem or UTP connections!. This you must do, and a low cost device that is also a *high quality* device, should be used. These devices are designed specifically for the protection of DC electrical surges and they are not used in series with a UPS anyway.

    Lightning, surge supressors, and telephone equipment

    (From: aa-2@deltanet.com@deltanet.com)

    Nothing will stop a good lightning strike, but there are things you can do to put the odds more in your favor.

    For telephone line protection, the place to start is where the phone line comes into your house. Locate the protector and verify you have a good ground close to it. Next, replace the standard carbon protector elements with gas tubes. These often look like large brass hex bolts with no wires attached, but the exact design will vary. Carbon protectors operate rather slowly; gas tubes ionize very quickly and carry large amounts of current. You may have to shop around your local telco supplier to find these. Strictly speaking, these are on the telco side of the demarc and you're not supposed to fool with them, but if you won't tell, I won't either. Or you could call your local telco and ask for the gas tubes...

    Then add your store-bought protector inside. Make sure it has a good ground, too. It can't hurt, and it might help. But the best place to try and stop the lightning is before it enters your house.

    Paul's Notes on Power Line Connected Devices

    The most common of these are so-called "wireless" intercoms and X10 appliance controllers.

    (From: Paul Grohe (grohe@galaxy.nsc.com).)

    The "Wireless" intercoms actually send 220 to 250 kHz signals across the power line. They pump about a volt or two into the line - then receive in the millivolt range. Obviously - the power line is NOT a good transmission medium.

    They worked fine years ago when most loads were mostly inductive (lamps, motors, transformers, etc).

    Nowadays, there are loads that essentially place small value capacitors across the line - most notably power strips and newer electronic equipment with switching supplies (Computers, TVs, VCRs, compact fluorescent lamps, etc). These "small" caps essentially short out any high-frequency noise on the power line. To make things worse, switching supplies and CFL bulbs run in the 40 to 80 kHz range, and can spray harmonics well into the 200 kHz range. Some channels will get knocked out by poorly filtered switching supplies or CFLs.

    Also, both intercoms need to be on the same service "leg". The majority of (US) homes are fed by a 120-0-120 feed. Half the home is on one leg, and the other half is on the other leg to "balance" the load. Even two outlets in the same room may be on different legs. The kitchen usually has the most of these "mixed" outlets.

    If the intercoms are on opposite legs, the signal has to traverse the transformer to get to the other leg. Obviously, with the inductance of the pole transformer and long power feed, the signal rarely makes it back.

    BTW: If the intercoms work better if a 220 VAC load, such as an oven, drier or stove is turned on - then they are defiantly on separate legs.

    X-10 remote controls also face a similar problem. Do a search on X-10 wireless controllers - there are many FAQs about signal problems and what causes them. There are devices that allow the X-10 signal to "bridge" between the two lines. Essentially a high-voltage, low value capacitor that must be professionally installed at the breaker box.

    One thing I have found is to NOT plug the Intercom/X10 device into the *same* outlet as a filtered outlet strip or TV/VCR/Computer/CFL. Instead, pick an outlet *between* the sending unit and the electronic loads.

    Think of "loads" as capacitive, and power line as slightly inductive - and you'll see why.

    As an alternative to power-line carrier - Radio Shack sells intercoms that use the phone line as the carrier - RS# 430-0483. Of course, they need a phone line too - but the performance is *much*, *much*, *much* better than the power line units.

    I originally tried the usual 'power line" intercoms - but encountered many problems with noise/interference from the computer and compact fluorescent lamps. I happened across a pile of some older-model phone-line intercoms at Goodwill and gave them a try - they worked perfectly with NO interference at all (although if you have DSL using "Microfilters" at each phone - you cannot use these intercoms or you must split off DSL at the phone box).

    The best they can do is to try other outlets - even if it means extension cords. Otherwise, they will have to switch to an "alternate" means since the power line is unusable. I have seen RF "intercoms" somewhere (900 mHz?) - so there are some available. But if phone lines are available at the locations they wish to use - then I would highly recommend the phone-line intercoms.

    Equipment dropped or abused

    I have heard of someone fighting off a would-be mugger with a tape deck but this is generally not a recommended practice. However, once it happens - your cassette deck fell off its shelf or you prized walkman fell from your hang glider (ok, maybe that will be too much even for miracles) - what should you do?

    Overall, electronic equipment - especially portable devices - are quite tough. However, falling or being beaten in just the wrong way can do substantial and possibly not immediately visible damage.

    If you take it in for service, the estimate you get may make the national debt look like pocket change in comparison. Attempting to repair anything that has been dropped is a very uncertain challenge - and since time is money for a professional, spending an unknown amount of time on a single repair is very risky. There is no harm is getting an estimate (though many shops charge for just agreeing that what you are holding was once a - say - tapedeck!)

    This doesn't mean you should not tackle it yourself. There may be nothing wrong or very minor problems that can easily be remedied.

    First, unplug the unit even if it looks fine. Until you do a thorough internal inspection, there is no telling what may have been knocked out of whack or broken. Electrical parts may be shorting due to a broken circuit board or one that has just popped free. Don't be tempted to apply power even if there are no obvious signs of damage - turning it on may blow something due to a shorting circuit board. If it is a portable, remove the batteries.

    Then, inspect the exterior for cracking, chipping, or dents. In addition to identifying cosmetic problems, this will help to locate possible areas to check for internal damage once the covers are removed.

    Next, remove the covers and check for mechanical problems like a bent or deformed brackets, cracked plastic parts, and anything that may have shifted position or jumped from its mountings.

    Carefully straighten any bent metal parts. Replace parts that were knocked loose, glue and possibly reinforce cracked or broken plastic. Plastics, in particular, are troublesome because most glues - even plastic cement - do not work very well. Using a splint (medical term) or sistering (construction term) to reinforce a broken plastic part is often a good idea. Use multiple layers of Duco Cement or clear windshield sealer and screws (sheetmetal or machine screws may be best depending on the thickness and type of plastic). Wood glue and Epoxy do not work well on plastic. Some brands of superglue, PVC pipe cement, or plastic hobby cement may work depending on the type of plastic.

    Cycle the the mechanism and check for free movement of the various moving parts.

    Inspect for any broken electronic components - these will need to be replaced. Check for blown fuses - the initial impact may have shorted something momentarily which then blew a fuse.

    There is always a slight risk that the initial impact has already fried electronic parts as a result of a momentary short or from broken circuit traces and there will still be problems even after repairing the visible damage and/or replacing the broken components.

    Examine the circuit boards for any visible breaks or cracks. These will be especially likely at the corners where the stress may have been greatest. If you find **any** cracks, no matter how small in the circuit board, you will need to carefully inspect to determine if any circuit traces run across these cracks. If they do, then there are certainly breaks in the circuitry which will need to be repaired. Circuit boards in consumer equipment are almost never more than two layers so repair is possible but if any substantial number of traces are broken, it will take a great deal of painstaking work to jumper across these traces with fine wire - you cannot just run over them with solder as this will not last. Use a fine tipped low wattage soldering iron under a magnifying lens and run #28 to 30 gauge insulated wires between convenient endpoints - these don't need to be directly on either side of the break. Double check each connection after soldering for correct wiring and that there are no shorts before proceeding to the next. Also see the section: Repair of printed circuit board traces.

    If the circuit board is beyond hope or you do not feel you would be able to repair it in finite time, replacements may be available but their cost is likely to be more than the equipment is worth. Locating a junk unit of the same model to cannibalize for parts may be a more realistic option.

    Once all visible damage has been repaired and broken parts have been replaced, power it up and see what happens. Be prepared to pull the plug if there are serious problems (billowing smoke would qualify). Determine if it appears to initialize correctly - without shutting down. Play a garbage tape to determine if there are any problems that might damage the tape. Listen carefully for any evidence of poor tracking, tape speed instability, or weak or muddy audio that might indicate that tape path alignment requires further attention. Listen as well for any unexpected mechanical sounds that were not there before.

    Very likely, the unit will be fine, you can replace the covers, and now find a more secure spot for it to prevent this sort of event in the future. Maybe hang gliding is just not for you!

    Decayed glue in electronic equipment

    Larger components like electrolytic capacitors are often secured to the circuit board with some sort of adhesive. Originally, it is white and inert. However, with heat and age, some types decay to a brown, conductive and/or corrosive material which can cause all sorts of problems including the creation of high leakage paths or dead shorts and eating away at nearby wiring traces.

    The bottom line: Most of the time, this stuff serves no essential purpose anyhow and should be removed. A non-corrosive RTV or hot-melt glue can be used in its place if structural support is needed.

    (From: Richard Rasker (r.e.rasker@student.utwente.nl).)

    Are you repairing somewhat older Japanese (Yamaha, Nikko, etc.) equipment, but the problem seems very obscure? Then maybe this may interest you:

    In some amplifiers and other equipment, the supply capacitors and other large pcb-mounted devices are secured in place by a type of gluelike substance, that after several years causes corrosion to all metal parts that it touches; eventually, the metal connections (like component wire leads and wire bridges) will fail.

    The substance in question is a dark yellow rubber-like compound, coloring brown and turning rather hard on the places where damage is done to other components. The only solution is to scratch it away completely and replace all components affected.

    I've already repaired five amps where this turned out to be the cause of trouble - with very vague symptoms, like a missing ground reference to an endstage, an on-board controller that wouldn't start up, etc. The first time it took me forever to find, so if this posting will make even one repair easier for someone, I'm already happy.

    Hope this makes life a (little) bit easier for all those people out there trying to repair stuff, instead of throwing it away :)

    P.S. My theory about this process: I think that the substance used is a rubber compound with an excess of sulfur, which will very slowly react with oxygen and moisture to form corroding chemicals (like sulfites). If anyone has a better theory (or the correct explanation), please let me know.

    (From: Jake Gray (jake79@hotmail.com).)

    I have found in a lot of electronical gear and more recently in my monitor. The glue has been designed mainly to hold leads and wires in place, also to hold capacitors in place.

    It eventually soaks up the moisture from the air, giving it a conductive effect and the places that it is located don't like having a conductor across them. And, as time goes on, the glue seems to carbonize and become an even better conductor.

    Just keep and eye out for it, it is like a creamy colour and remove it ASAP.

    With many appliances, especially those with many IC's, I have found that with the removal of the glue, they work fine.

    Repair of printed circuit board traces

    In most cases, a functional repair - using wire to bridge the breaks soldered to conveniently located pads - is all that is needed. This will be at least as reliable as the original foil wiring if done properly. However, there are those times when a complete restoration is desired:

    Note: If the original cause was chemical corrosion rather than mechanical, ALL of the offending material must be removed and/or neutralized before any sort of reliable repair can be attempted!

    (From: MKILGORE (mkilgore@aol.com).)

    Yes, you can repair damaged/lifted conductors and pads on circuit boards. If you would like to repair the damaged area professionally, track repair kits are available from sources such as Pace. These repairs once completed are almost undistinguishable from the original work. Damaged pad replacement - Using a scalple or Xacto knife follow the run attached to the pad back to a point where it is still firmly secured, at a 45 degree angle, cut the trace loose and remove it from the board and discard. Scrape any solder mask from the end of the trace back about 3 trace widths, and clean the area with an ink eraser, then tin the area. Select a pad with trace from the kit ( various sizes are included ) position it in place of the damaged run and form it so it follows the contour of the board to the 45 degree angle cut and rests on top of the original trace by about 2 trace widths. Now prepare a small amount of two part epoxy and flow it on the board where the replacement conductor will lie, do not get any on the tinned conductor. Lay the replacement conductor in place and allow the epoxy to dry, this can be speeded up with a heat lamp. Once dry simply apply flux to the joint and solder the two pieces together. If this was a plated through hole, or strength is an issue, the kit contains eyelets which can be installed through the board. --- However, if the trace you wish to repair is merely lifted you can simply use the epoxy and secure it back in place.

    Circuit repair where a pad has been lifted due to mechanical stress

    This might be the case where someone tripped over the AC adapter cord of a walkman or laptop computer thus ripping the jack from the circuit board.

    (From: KIRTO (Kholson@cris.com).)

    As you will see in the following, I recommend using something other than the pad to get that strength.

    I suggest you provide mechanical connection between the jack and the board so that the jack can't move with respect to the board.

    Techniques include a wire strap over the component near the back and soldered to the board like you see on crystals or adhesive under the jack like you see on large caps in midboard.

    Another possibility is to put a rubber bumper atop the jack so that the front cannot tip inward when it's in the case. A stick-on foot might be a start, with whatever 'foot surgery' is needed to fit.

    If the jack has a rim near the front (like a std keyboard connector) you might be able to put triangular braces on either side of it with adhesive and some stiff rubber or plastic.

    I have seen this problem happen when someone trips on a cord and thus pulls the connected jack at a sharp angle with high force. Warn the customer about this possibility, and suggest using an extension cord on the power adaptor.

    (From: Hank Sievers (textax@aol.com).)

    The best way that I can think of is to bend down whatever part of the leg extends through the board and bridge with a heavy bare wire and plenty of solder to as much of the nearest part of the trace (scraped to the copper, of course) as you can. Then, for good measure put a drop of magic glue or some silcone sealant where the leg comes through the hole. Should be stronger than the original.

    I am a charter member of the the 'down-to-the-component-troubleshooting fraternity', since I am naturally curious and fortunate enough to have the time, since I am retired. However, I can see where it is often important to the bottom money line, not to spend too much time on a repair and so replace the entire unit. Time is money also!

    Boombox or other equipment went to the beach (sand and/or surf)

    A (former) relative took your boombox to the beach this summer and now it has sand or perhaps salt in it. Or, maybe you could not resist "sing'n in the rain" and a big bus went by without slowing. Now neither of the tape decks will play. Can this possibly be fixed? Will it be worth the effort?

    Unless this is a really expensive sophisticated unit, I doubt whether it will pay you to take it anywhere for repair. Furthermore, as with equipment that has been dropped or physically abused, few repair shops will be inclined to touch the job. They really don't like challenges of this sort.

    That leaves you!

    If saltwater was involved in a significant way, you can probably forget it. Without immediate attention, saltwater corrosion can set in very quickly and attacks electronic components, circuit board traces, cable wiring, and mechanical parts. The only thing worse is damage caused by forgotten, leaky batteries.

    Although it is probably too late, the first thing to do when electronic equipment gets wet is to remove the power source - switch it off and pull the plug or remove the batteries if possible. Don't be tempted to apply power until you have determined that it is completely dried out. If power was on when the 'incident' took place, then electronic damage may have already resulted which will not be apparent until after cleaning, drying, and lubrication.

    The following description assumes a dual cassette boombox. Adjust as appropriate for your patient:

    If the tape decks are totally dead, you may have serious electronic or corrosion which will make any salvage unlikely. If they sort of move (or even twitch a bit) but the sound is erratic, weak, fluttery, etc. then there may be hope. (Of course, if it got wet, you should not have done this test until everything was cleaned and dried!)

    NEVER use strong solvents for any cleaning. These may attack plastic parts or cause internal damage to electronic components.

    Mechanical intensive care:

    1. Remove the tape decks. This will be a pain but otherwise you will not be able to get at everything. Make as many as drawings as needed so you will be able to reassemble.

    2. Make a drawing of the belt routing, remove the belt(s), wash and dry them, label and set them aside.

    3. Use a soft brush (like a paintbrush) to dust out as much sand as possible. Hopefully, you can get it all this way. A vacuum cleaner with a wand attachment may prove handy to suck out sand. Don't use high pressure compressed air - it will just spread the sand around. Any grease or oil on which sand has collected will need to be totally removed and replaced with fresh lubrication.

    4. If there is evidence of salt (remember, I said forget it...but), you will need to wash it off. Yes, wash it. Keep water out of the motors. Use low pressure compressed air (a blow dryer on low heat should be fine) to dry so that it does not rust. Ditto if it is still wet with contaminated liquid (we won't say where this came from), wash with fresh water to remove all traces of it as quickly as possible. A final rinse with 91% or pure isopropyl alcohol will decrease drying time and should not damage mechanical assemblies. Degreaser may be used if it is safe for plastic and rubber parts.

      Lubricate all bearing points with a drop of light machine oil - electric motor oil, sewing machine oil, etc. (Never never never WD40). Lubricate gears, cams, and sliding parts with a light plastic safe grease.

    5. Replace the belts and reinstall the tape decks.

    Electronic intensive care:

    1. Remove the circuit boards and label the connectors if there is any possibility of getting them mixed up. If the circuit board(s) are soldered to the rest of the equipment, then you will have to improvise.

    2. Wash with water and dry thoroughly. This does work. I use it routinely for degunking remote controls and rubber membrane keypads, for example. The most important objective should be to get corrosive liquids off the components and circuit traces as quickly and completely as possible. A final rinse with isopropyl alcohol will decrease drying time. However, there is a slight risk of damage to sensitive electronic components should some be trapped inside. Moisture will be trapped in controls, coils, selector switches, relays, transformer cores, connectors, and under large components like ICs. Pat dry, then use warm air from a hair dryer (or heat gun on low) to completely dry every nook and cranny. DO NOT operate until everything inside and out is thoroughly dry.

    3. Inspect for damage due to short circuits including blown fuses, fried components, and melted traces. These will need to be repaired or replaced.

    4. Use spray contact cleaner on the switches and control cleaner on the user controls and adjustment pots. DO NOT turn the internal adjustments without precisely marking the original positions - else realignment will be needed. Exercise the user controls to help the cleaning process.

    Once everything is reassembled, power the unit up and see what happens. Be prepared to pull the plug or pop the batteries if there are serious problems. Attempt to play a garbage tape to determine if there are any problems that might damage the tape. Look and listen for any abnormalities which may require additional attention. There could still be electronic faults not repairable without schematics and test equipment.

    Obviously, this description is very simplistic. The important thing is to get every last grain of sand, salt, and other contaminants off of the mechanisms quickly.

    Similar comments apply to equipment that went for an actual swim - you dropped your portable CD player in the toilet. The most important objective is to clean and dry it as quickly as possible and then relube any motor and other bearings. Use your judgement as to the severity of the dunking in terms of how deeply the liquid penetrated. Surface moisture will not hurt anything as long as it is dried up quickly. If you left it soaking on the other hand....

    As noted above, moisture may collect inside certain electronic parts and it is essential that these be dried completely before attempting to apply power to the unit. If you do not, at best it will not work properly and you may do additional serious damage due to short circuits.

    For the mechanics, the same applies though this is trickier since certain parts need to be lubricated and these may not be readily accessible or obvious. Don't be tempted to overdo the lubrication either - too much is worse that too little.

    For high tech devices like CD players, some parts of the internal optics or shielded DC-DC convertors may be impossible to access and clean of scum.

    Salt water salvage

    (From: John Baker (jbaker@flash.net).)

    I have repaired equipment that has been soaked in salt water and it depends on what type of components it has on the boards. If they have any batteries on them, get them off as soon as possible. transformers are usually good for rusty paperweights. Get the boards out of the salt water and into fresh water ASAP. I have not found any chemicals that will remove the salt deposits and leave the traces. The best bet is to use a small nylon brush along with a chemical called Flux Off-nr, there are several types of Flux-Off, get the one that does not harm plastic parts, it is not as strong but it workes just as well in this case. From there it takes a lot of time. Use the brush and remove all salt deposits, try and get under all components, especially IC's. Most components can take being under salt water with no damage, it is the batteries and metal that cause problems.

    Fil's notes on rescuing soggy equipment

    (From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org).)

    Greetings. I've recently had the opportunity to rescue several rather expensive electronic units after the owner flipped the canoe and spilled the beans, so to speak.

    The dead units were: a Casio solar-powered calculator, a car-alarm key ring transmitter, a 10-satellite GPS unit (yowser!), and some smaller items.

    Note: GPS unit was waterproofed and did not suffer much.

    Solution (sorry, pun) was: purchase 1 gallon of distilled water, disassemble the units and submerge the PCBs (and keypads and displays) in containers. The devices were left soaking for more than 20 minutes. Then, they were removed and dried with a hair dryer (and fan for less expensive items).

    Results: excellent. All items have been brought back to life. Some *did* require purchase of new (rather expensive) Lithium batteries but that was a small price to pay.

    Hint: It is highly useful to have a brush to clean the area between ICs' pins after 10+ minutes of soaking. This helps to remove any minerals that are not as soluble in water as others. This is more of an issue if the items came in contact with flood-stage stream than a sinkful of tap water. :-)

    Observation: devices that were "on" at the time of the dunking were the most damaged and required the most time to soak. Batteries had to be replaced since they *all& started to leak.

    REALLY cleaning electronic equipment

    The following is probably excessive for most needs and should be used with caution since there are some types of components which will not take kindly to forced hot water cleaning. In addition what is mentioned below, mechanical assemblies like motors and solenoids should be removed and dealt with separately. And, of course, any moving parts that are left in place should be thoroughly dried as soon as possible and then lubricated with the proper oil or grease.

    (From: Gray Frierson Haertig (gfh@haertig.com).)

    I have had excellent results cleaning electronics in the dishwasher. I try to do a bit of disassembly so that as much of the instrument is exposed as possible. If you can separate chassis from electronics, so much the better. I have generally avoided putting unpotted transformers and inductors and the such through the wash. I either hand clean those boards or dismount the sensitive item. Mechanical parts can be run through the whole cycle, if your water is reasonably soft. A second rinse cycle doesn't hurt. The electronics should not go through the heat dry cycle. They should be thoroughly flushed in deionized or distilled water after they come out of the washer to prevent mineral and salt deposits. Then go after it with a blow dryer set to low heat, or if you're blessed with sunshine, smear on the cocoa butter and let them work on their melanoma.

    Reviving old (antique) equipment

    If you have a true antique - really old, and valuable, you should refer to the extensive literature available on this subject. The following applies more to that 30 year old record player/amp found in the storage loft of your garage during spring cleaning.

    Common problems relate to two types of components: vacuum tubes (valves for all of you on the other side of the lake) and capacitors (paper and electrolytic type). Push all the tubes down in their sockets as well - they will work their way loose with non-use and vibration. However, thorough cleaning of all socket and switch contacts, and controls will almost certainly be needed.

    WARNING: the voltages inside tube type equipment can exceed 400 V - and contact with that can be real painful not to say dangerous. AC-DC type sets are not isolated from the power line. (In some really old equipment, even the chassis may be tied to one side of the line). This could also happen as a result of a shorted component. The electrolytic capacitors can hold a charge for quite a while. Read, understand, and follow the recommendations in the document: Safety Guidelines for High Voltage and/or Line Powered Equipment. Use extreme care when probing or even touching anything. This isn't 5 V logic!

    Vacuum tubes:

    It is not possible to fully test vacuum tubes without proper equipment but the inspection and tests below will find most bad tubes but will not pick up weak tubes. As a side note, when a repair shop replaced tubes, perhaps 20% of the tubes they replaced were actually bad (I know because the local TV repair shop's trash can was a favorite hangout on pickup day and nearly all the tubes I scrounged tested perfectly good on a real tube tester once they were washed of coffee grounds and cigarette ash!) Whether this represented legitimate preventive maintenance or just IPM - Increased Profit Margin, I really do not know.)

    1. Look for a silvery metallic spot somewhere inside the tube. This is the getter and is there to remove the last traces of gasses. If you see this, the vacuum is intact. If it is milky white or red, the tube has lost its vacuum and is dead-dead.

    2. Use an ohmmeter to test for filament continuity. The nice thing about tubes (aside from their cheery glow) is that you can see inside (at least for the ones with a glass envelope) and locate the filament connections by tracing from the pins - it will be the whitish fine wire in the center of each of the tube sections. (The filament is almost always pins 3 & 4 on a 7 pin tube, 4 & 5 on a 9 pin tube, and 2 & 7 on an 8 pin tube.)

    3. You can check for inter-element shorts (but not at normal operating conditions) with a VOM or DMM. For glass tubes, even without a tube manual, you should be able to deduce which elements are supposed to be isolated by visual examination.

    Now, just jump into your time machine, back about 20-30 years should do it (remember?) when every corner drugstore and TV repair shop had a tube tester. There is, of course a good chance that your local TV repair shop still has one (if they can find it under an inch layer of dust) and it may even work.

    Capacitors and resistors:

    If you just dug this thing out of the attic, it is very likely that electrolytic capacitors have dried up and paper capacitors have turned leaky. Professional restorers will often install modern replacements for all of these capacitors without even testing the old ones. To maintain the authenticity of the vintage equipment, they may actually remove the guts of the old capacitors and mount the new ones (which are much smaller anyhow) inside the original cans.

    Old carbon resistors can absorb moisture and change value. If your measurements do not agree with their marked rating based on their tolerance, consider replacements. However, if within, say, 20 %, for now, leave them alone.

    Sockets, switches, and controls:

    Vacuum and/or use a small paintbrush to remove dust, spider webs, dead insects (and anything larger).

    Remove each tube (or transistor) one at a time and use contact cleaner on the sockets. Tubes are usually keyed against incorrect installation. However, for transistors, make sure which way they go! You don't want to make a mistake. Use contact cleaner on all the switches and exercise them to help the contact cleaner do its job. Use control cleaner on all the potentiometers and rheostats and rotate them back and forth to help clean the track. Put a drop of oil into the bearings of any non-enclosed (multiplate) variable capacitors. Lubricate mechanical dial pointers, pulleys, and and other similar mechanical parts.

    Testing (use an isolation transformer with AC-DC line connected sets):

    Much of this old equipment had schematic diagrams pasted to the cover - really handy if the paper hasn't totally disintegrated.

    Turn on the power but be prepared to pull the plug in a hurry if, for example, a capacitor should decide to blow up (this shouldn't be a problem if you replaced them all unless some electrolytics are in backwards).

    It is probably best to use a Variac to increase the voltage gradually. In fact, this will help to 'reform' old electrolytic capacitors that have developed excessive leakage. However, by 'gradually', we may be talking hours or days to reform capacitors! I would still recommend replacement even if this appears to work.

    Do the filaments light up? If your equipment has a power transformer, the filaments are probably wired in parallel, so if one tube is out, that tube is bad (or its socket). If they are all out, then the power transformer or AC line input is bad.

    If it is an AC-DC set like a table radio, then the tube filaments are wired in series. If one is bad, they will all be out. Get out your ohmmeter, pull each tube, and check it for filament continuity.

    Assuming the filaments check out - all sections glowing (for metal tubes, feel the case for warmth after a few minutes though this won't guarantee that all sections are alive) when power is applied:

    WARNING: It is possible for metal cased tubes to develop a short between one of the high voltage electrodes like the plate and the metal case. Test with a voltmeter before grabbing one of these and keep that other hand in your back pocket!

    Check for DC voltages out of the power supply. There will be big filter capacitors - check across those. Watch out: we are talking several hundred volts and BIG capacitors - ouch.

    With no signal, check plate voltages on the various stages - there should something. If you measure 0, then a plate resistor or coil could be open or the tube may be shorted.

    The rest is just basic troubleshooting. Think of the vacuum tubes as oversize high voltage depletion mode FETs (field effect tubes, why not?). This is not much different than modern equipment except for the bites the relatively high voltages can take out of your hide.

    There are some links in Sam's Neat, Nifty, and Handy Bookmarks to vacuum tube information and troubleshooting.

    Additional comments on old equipment restoration

    (From: Carl Ratner (artdeco@bway.net).)

    A good place to post problems is rec.antiques.radio+phono. There are often discussions there about fixing vintage electronic gear.

    Many long books have been written about fixing old radios! If you don't want to do a lot of reading and learn a lot of theory, here are some practical tips: First, give the radio a thorough physical inspection with the power disconnected. Use your eyes and your nose. Look carefully for broken or disconnected wires, charred components, damaged insulation, etc. If you see wax dripping from a transformer or if it smells burnt, there has been an overload of some sort that will need to be identified. If the set has an internal antenna, make sure that it is connected. If an external antenna is required, connect a long piece of insulated wire, say 15 feet, and lay it on the floor. Old sets will play very weakly or not at all if the antenna is missing. Always replace the power cord if it is deteriorated.

    In radios of 1930s vintage, it's very likely that all wax paper capacitors, as well as the electrolytic capacitors, are bad. First thing to do is replace all the wax paper ones with modern mylar types. If you have the tall metal can electrolytics, you can put modern ones under the chassis (the new ones are tiny). However, you must disconnect the old ones from the circuit... don't bridge the new ones across the old. Be sure to observe polarity of electrolytics. You may leave the old cans in place to retain original appearance. BTW, the old square mica capacitors seldom need to be replaced unless the cases are cracked open of they have other obvious damage.

    Even if some of the old wax paper capacitors are still good, they are likely to fail within a few days if you start using the set. I've restored hundreds of old radios and have learned this from experience. Get them all out of there and save yourself a lot of trouble.

    You should also check the value of all the carbon resistors in the set. They tend to go high or open with age. Replace the bad ones with modern equivalents (same resistance and wattage). You may have to disconnect one side of a resistor when testing it, as the associated circuitry can cause a low reading. However, if a resistor reads way too high, you don't have to bother disconnecting it for testing as it is definitely bad.

    Your set should start playing quite well after you change all the capacitors and possibly some resistors. You noted that you had changed the tubes, and I'll assume that all the replacements are good. Tubes don't fail nearly as often as people would expect, however, and it's possible that the set's original tubes were OK. Once you get the set working, you can substitute the old tubes one at a time to see if the set continues to play. Then just keep the good ones as spares.

    Set still dead? If you have a multimeter, check the B+ voltage. The audio output tube's plate connection is a good place to do this. This can be 250-350 hundred volts in a transformer set, so work with care. If B+ is absent or some very low value, you have a problem in the power supply. (If you tell me the tube numbers in your set, I can give you some of the pinouts for testing) If the rectifier tube is known to be good, and you have already changed the electrolytics, then you may have a bad power transformer (large black box, usually near a back corner of the chassis. These are hard to find nowadays and very costly. I'm assuming here that you don't have a B+ short somewhere else in the radio. You will know about that because something will be smoking if such a short exists!

    There are other components that can fail. Inspect the speaker for physical damage. You can test the voice coil and field coil for continuity. Replace if open. A modern permanent magnet speaker can be substituted for an old field coil speaker, but a power resistor of abut 1500 ohms, 20 watts must be added to replace the field coil. Dirty volume controls and band switches can cause noisy, weak or intermittent sound too. Clean them with a good spray cleaner such as Deoxit D5. Avoid the "tuner cleaner" that is sold at Radio Shack. It is worthless for fixing old radios.

    As a final step, your set may need an alignment. This consists of adjusting all the tuned circuits to factory specifications to obtain the best possible performance from your set. You need a signal generator and an output meter to do this properly. It is strongly recommended that you do not twiddle any screwdriver adjustments on the IF transformer cans or elsewhere in the set unless you know exactly what you are doing. Misadjustment will cause the set to play very poorly or not at all.

    End of short course in fixing old radios.

    (From: R. G. Keen.)

    1. Use a battery or ohmmeter to verify that the speaker clicks when electricity hits it.

    2. Disconnect the output transformer primary and use the battery on the primary to verify that it makes the speaker click, albeit faintly.

    3. Power the amp. verify that the plate(s) on the output tube(s) are sitting slightly below B+, and that cathode is near ground, grid more negative than cathode.

    4. Touch a probe to the grid of the output tube, listen for a click in the speaker. No click means that the output tube or it's surrounding circuitry is bad.

    5. Assuming that (4) worked, go one tube back up the signal chain at a time, touching grids and listening for clicks. When the clicks stop, that tube or the circuitry around it is bad.

    6. When you find the bad one(s), measure all the resistors and check the capacitors for leakage. Measure the tube pin voltages for plate high, cathode low and grid less than cathode. sub in a new tube.

    7. It could be an open volume or tone pot between stages. Also a bad solder joint. remelt and touch with a bit of rosin core solder every joint in the bad stage.

    (From: John Mitchell (j.b.mitchell@qmw.ac.uk).)

    Get a hold of the "The Amp Book" (or something like that) by Aspen Pittman. It's stuffed full of dozens and dozens of tube amp schematics plus other info on mods servicing etc.

    Capacitors in old equipment

    (From: George R. Gonzalez (grg@umn.edu).)

    I used to repair mostly oooold radios from the 1930s and 40s. Now I'm doing more of the newer stuff, including test equipment and stereos from the 60s and 70s. Here's my rundown of what needs replacing capacitor-wise:

    I think I'm going to stock up on small electrolytics, as those seem to only have a 30-year life, even in the cooler-running more modern equipment.

    Tube amp Web sites

    Sites with tube amp design, troubleshooting, info, links:

    (From: Duncan Munro (postmaster@muffy.demon.co.uk).)

    (From: Jan B. Jensen (jbj@lif.dk).)

    TV/VCR combos

    These hybrids which include both a TV and VCR (and sometimes other stuff as well) seem to combine the worst of all possibilities. Although, in principle, the idea of a combination TV/VCR sounds good - no cabling to worry about, ease of use, compatibility assured, the result may be less than meets the eye. While TV/VCR combo units do include both a TV screen and a VCR transport, very often there is only a single shared tuner so that viewing and recording of different programs is not possible unless one is from an external baseband video source (assuming there is a suitable input jack) like - you guessed it - a VCR or laserdisc player.

    If either the TV or VCR poops out and needs repair, the entire unit may be unusable either because of shared circuitry or because the whole thing is in the shop. Construction quality tends to be shoddy and some designs are poor to begin with. Finally, as if this is not enough, servicing is difficult and painful because everything is crammed into a single compact (at least that is a good feature!) unit.

    Refer to the appropriate documents for your particular problems.

    Boomboxes and compact stereo systems

    These combine a stereo receiver and a single or dual cassette deck, and/or a CD player or changer, and a pair of detachable speakers, into a single unit. Most are fairly portable but larger boomboxes and compact stereos may require a forklift to move any great distance.

    While the individual subsystems - CD player for example - are usually relatively self contained electrically except for a common power supply, mechanically, everything tends to be jumbled together - even on units that have an outward appearance of separate components. Both cassette transports are usually driven from a single motor. Getting at the CD player may require removal of both cassette decks, audio amplifier, and power supply. Working on these is not fun. As usual, take careful notes as you disassemble the unit and expect it to require some time just to get to what you are after. Be especially careful when removing and replacing the individual modules if printed flex cables are used for interconnections.

    Refer to the relevant sections on cassette transports, loudspeakers, and power supplies for problems with these units. Refer to the document: Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives for CD specific problems.

    Since these do get abused - bumped, dropped, dunked, etc., bad connections, and other damage is very common. See the sections: "General intermittent or erratic behavior" as well as "Noisy or intermittent switches and controls".

    Design to discourage repair

    Here is a description of the pain involved in attempting to get at the CD player part of a Garrard boombox. Sadly, this is all too typical of 'Getto Blaster' construction.

    (From: BELJAN E (lvpy67c@ix.netcom.com).)

    I managed to get the whole Garrard mess disassembled (this thing is a major pain to service). The CD mechanism is removable, but just try it. This boombox has all sorts of modules: main board, display, cassette, radio, power supply, and CD are all separate. The problem is the way it is designed you simply cannot reach all the connectors to get the CD player out. If I could get the CD player out, I could disassemble it and find the solution. By the way, voltage to CD section appears OK. I would not have been able to find loose connections had there been any. I put it back together, CD still dead, everything else still works. It is convenient to service only if you intend on replacing the entire mechanisms (possibly Garrard's motive?). If I really needed to, I could simply detach the CD mechanism and replace it. I wouldn't bother. I see they now have Garrard Boombox with Dual CD players, and one with all sorts of features, one with detachable speakers and so on. This is a mystery, with the voltages OK, it would seem that there would be a loose connection, but none are visible (remember I cannot get the whole thing out).

    I say this thing is a pain to service, here is why:

    1. You must have an 8 inch long thin phillips screwdriver to disassemble it.

    2. You must remove the cassette player to reach the Display.

    3. You must remove the display to reach the switches.

    4. You must remove the switches to reach the CD mechanism.

      An interesting note: the display modules are connected to the CD mech, along with the headphone module, they work fine.

    5. you must unscrew the CD player from behind, then attempt to slide it forward, while it is connected to the main board from behind with white push on connectors. You get it halfway out, careful now, you don't want to damage the Cassette deck, which is connected somewhere out of visibility.

    6. Once you slide it forward, you must try to loosen the slide on connectors without dropping the whole mechanism on the main board. (you need 6 hands and screwdrivers to try to do this.

    7. On top of all that, the Whole Front of the unit is hanging there, connected also out of site

    This unit is incredible. Truly incredible. It is easy to replace whole components, but servicing?

    Panel lamps out

    In the old days, this was due to the failure of easily replaceable and widely available miniature incandescent lamps. Even today, may displays are not LEDs as you might think but LCDs with backlighting provided by - you guessed it - incandescent lamps. Unfortunately, they are rarely easily replaceable and or as widely available.

    This will be particularly likely if the display color is anything but the most common for LEDs - red. You might find green LEDs but will not likely find orange and certainly not blue or purple. LEDs would not be orange because the additional cost of orange LEDs would not translate into increased sales of boomboxes (or whatever). Blue LEDs are very expensive and purple ones do not exist.

    The bulbs are replaceable. Getting at them may be easy or require entirely disassembling the unit. Soldering may be required as the manufacturer saved a nickel by not providing a socket. They may be tiny and special - try places like MCM Electronics for replacements.

    If they are really red LEDs or vacuum fluorescent displays, then the most likely problem is a bad connection or other physical damage.

    Adjusting station/channel settings on tuning dials

    So 95.7 MHz comes in a 100.1 MHz on the dial.

    Don't touch any of the trimmers on the tuning capacitor! They didn't magically change their settings. Just move the pointer on the dial cord to match a known centrally located station. If it is glued, you may have to carefully break the bond between the pointer and the dial cord. Then put a drop of household cement to fix its position when you are satisfied with the adjustment. Only if the ends of the dial are way off frequency should you consider anything beyond this mechanical fix.

    Caution: Be careful! Should you accidentally cut the dial cord or have it pop off of the pulleys, you will have a much bigger job ahead of you. In this unfortunate circumstance, see the section: Repairing a broken dial cord or tuning gang wire.

    Repairing a broken dial cord or tuning gang wire

    With age, use, or through some mishap, it is inevitable: your analog dial no longer works because the string that runs between the tuning knob, variable capacitor, and dial indicator has broken. How does one repair it?

    The simple answer is: very carefully! :-)

    Demonstrating your skill in stringing dial cords is one of those rites of passage that has (thankfully) pretty much disappeared :-). Usually, it succumbs to a bit of logical thinking and carefully placed bits of tape to keep the entire mess in place until the last knot is tied!

    These are a royal pain - especially if you do not know the original routing. In this case, some of it is going to be by trial and error. Some of my learned-the-hard-way tips:

    1. Major electronics distributors will actually be able to supply dial cord material without making too much of a face though they may have to go into a dusty old bin to locate it!

    2. Start at the variable capacitor pulley. Tie your favorite knot and secure it with some semi-flexible adhesive like Duco Cement(tm) or windshield sealer.

    3. Route the cord around the appropriate idlers and the tuning knob shaft.

    4. As a default, 3 turns on the tuning knob shaft seems to be common. If there isn't enough space for 3 turns, use 2 turns. If it slips with 3 turns, use 4 turns.

    5. If in doubt about the direction, determine which way it will end up turning the variable capacitor. Clockwise rotation of the tuning knob should increase the channel frequency by decreasing the capacitance - plates separating.

    6. Use bits of electrical tape or putty to keep the cord from popping off of the idlers, etc., until you have it firmly attached to the spring on the other side of the variable capacitor pulley.

    7. Once you are happy with the routing, pull it tight enough to stretch the tensioning spring about half-way. With the cord held in place with your finger, confirm free and smooth movement throughout the entire tuning range.

    8. Tie the cord off and seal it as in (1) above.

    9. Install the dial pointer - it usually just clips on. Tune a known station and slide the pointer along until it lines up with the correct frequency. Use a dab of sealer to keep it from wandering off.

    Congratulations! You are done. Hopefully, only 3 or 4 iterations were needed. Now, if you need to do this again, it will be easier! And, your supply of tuning cord will probably last centuries.

    One more gotcha: Don't attempt to solder circuitry near a dial cord - get your iron near it and the stuff often used melts instantly - much fun! Push it out of the way or shield it with something.

    Revival of dead or tired remote control units

    There are two types of problems with hand held remote controls: they have legs of their own and they get abused or forgotten. I cannot help you with walking remotes.

    Where response is intermittent or the reliable operating distance is reduced, first check the batteries and battery contacts. If some buttons are intermittent or dead, than the most likely cause is dirty or worn contacts under the rubber buttons or on the circuit board.

    If there is no response to any functions by the TV or VCR, verify that any mode switches are set correctly (on both the remote and the TV or VCR). Unplug the TV or VCR for 30 seconds (not just power off, unplug). This sometimes resets a microcontroller that may have been confused by a power surge. Confirm that the remote has not accidentally been set to an incorrect mode (VCR instead of TV, for example). If it a universal type, it may have lost its programming - reset it. Make sure you are using the proper remote if have multiple similar models.

    Test the remote with an IR detector. An IR detector card can be purchased for about $6. Alternatively, construct the IR detector circuit described in the companion document: Notes on the Troubleshooting and Repair of Hand Held Remote Controls.

    If the remote is putting out an IR signal, then the remote or the TV or VCR may have forgotten its settings or the problem may be in the TV or VCR and not the hand unit. The following is just a summary - more detailed information is available in the companion document: Notes on the Troubleshooting and Repair of Hand Held Remote Controls.

    Problems with remote hand units:

    All except (1) and (2) require disassembly - there may be a screw or two and then the case will simply 'crack' in half by gently prying with a knife or screwdriver. Look for hidden snap interlocks.

    1. Dead batteries - solution obvious.

    2. Corroded battery contacts, Thoroughly remove chemical deposits. Clean contacts with pencil eraser and/or sandpaper or nailfile.

    3. Broken connections often between battery contacts and circuit board, possibly on the circuit board - resolder.

    4. Bad resonator or crystal - replace, but diagnosing this without an oscilloscope may be tough. Broken connections on resonator legs are common.

    5. Dirt/spills/gunk preventing keys from operating reliably. Disassemble and wash rubber membrane and circuit board with water and mild detergent and/or then alcohol - dry completely.

    6. Worn or corroded contact pads on circuit board. Clean and then use conductive Epoxy or paint or metal foil to restore.

    7. Worn or dirty pads on rubber keypad. Clean. If worn, use conductive paint or metal foil to restore.

    8. Cracked circuit board - can usually be repaired as these are usually single sided with big traces. Scrape off insulating coating and jumper breaks with fine wire and solder.

    9. Bad LED. If IR tester shows no output, remove LED and power it from a 9V battery in series with a 500 ohm resistor. If still no output, replace with readily available high power IR LED. Otherwise, check driver circuits.

    10. Bad IC - if it is a custom chip, forget it! Failure of the IC is usually quite unlikely.

      (The following is from Duane P Mantick:)

      An awful lot of IR remotes use IC's from the same or similar series. A common series comes from NEC and is the uPD1986C which, incidentally is called out in the NTE replacements book as an NTE1758. A lot of these chips are cheap and not too difficult to find, and are made in easy-to-work-with 14 or 16 pin DIP packages. Unless you have no soldering or desoldering skills, replacement isn't difficult.

    There are a large variety of universal remotes available from $10-$100. For general TV/VCR/cable use, the $10 variety are fine. However, the preprogrammed variety will not provide special functions like programming of a TV or VCR. Don't even think about going to the original manufacturer - they will charge an arm and a leg (or more). However, places like MCM Electronics do stock a variety of original remotes - prices range from $9 - $143 (Wow $143, for just a stupid remote! It doesn't even have high definition sound or anything exotic). The average price is around $40.

    Problems with keypads or touchpanels

    Most common are moisture problems followed by physical damage:

    Very often, a little overzealous cleaning results in moisture trapped inside a not quite perfectly sealed membrane keypad or touchpanel.

    First, of course, dry off the exterior as best you can. Any moisture that seeped inside may be difficult to remove without surgery - which is definitely not something you want to undertake as the long term reliability will be compromised.

    I would recommend waiting a while - a week may be required - for it to totally dry out. You could also try confirming across the touchpad contacts with an ohmmeter that there is still low resistance (even 10s of K ohms may look like a button press). It is nearly impossible to speed up this process without subjecting the device to conditions that may harm the device - heat and/or vacuum. You possibly try something like isopropyl alcohol in the hope that it will displace the water and dry quickly. I do not know if this will be safe in every situation, however.

    Of course, it is also possible that are other problems but I have seen these things take a very long time to dry out.

    However, significant damage - a membrane type touchpad is punctured - may require replacement unless you can repair the internal wiring. The connections are usually made with flex-cables which are difficult or impossible to repair. See the section: Repairing flexible printed cables. Damage to any membrane buttons may result in stuck buttons or improper operation of other buttons.

    Repairing flexible printed cables

    It seems that more and more consumer devices from pocket cameras to laptop computers are being built with miniature multiconductor flexible printed cables. Very often one or more traces to develop hairline cracks due to repeated flexing. In addition, damage from moving circuit boards and modules during servicing is all to common.

    Needless to say, repairing any kind of flex cable is a real pain!

    Caution: many devices like calculators have printed cables that use a material that will not take solder and are glued rather than soldered at their ends - the logic board and LCD panel, for example. Repair of problems with the cables is virtually impossible. Take great care when working inside of devices with this sort of cabling to prevent damage to the cables or their termination.

    With types like these in particular where soldering is not possible at all, the use of conductive paint, conductive Epoxy, or the stuff in a windshield defrost heater repair kit are worth trying.

    For the metallic conductor types, I have succeeded by carefully scraping the plastic off with an Xacto knife and then soldering fine wire (#30 gauge wire wrap for example) to the traces. This presumes that the conductors on your cable will even take solder. I then cover up the joints with a flexible sealer for electrical and mechanical protection.

    However, you need to make sure that the wire you use can be flexed or that the joint is set up in such a way that the wire does not flex much - else you will just end up with broken wires pretty quickly.

    Soldering from end point to end point if possible may be preferable. Even going to only one endpoint would reduce the risk of immediate damage and reliability problems in the future.

    With multiple traces broken or damaged, you are probably better off replacing the cable entirely.

    Where the break is near one end and the equipment will be happy with a cable that is slightly shorter, it may be possible to cut off the bad part, carefully scrape the insulation from the appropriate side exposing a new set of contact strips to go in the socket.

    (From: Steinar Botten (sbo@nera.no).)

    I just fixed an electronic kitchen scale where the glued-on flex cable had begun to come loose from the LCD display, causing some of the segments to grow faint and disappear, while others showed when they shouldn't. In my first attempts I used conductive paint, but I couldn't get the viscosity right so that the paint didn't spread and short-circuit some of the connections. So I removed and discarded the flex cable and cleaned the tracks on the PCB where the cable had been attached. I searched through my collection of IC sockets and found one type with "fork-type" contact springs that could be removed from the socket and that fit snugly over the glass edge of the display. The spacing of the contact points of the display left just enough room for insulation (I used linen thread because the subsequent soldering would have melted plastic tape) between the contact springs. After having fixed the display back on the PCB with double-sided tape I soldered fine copper wire between the springs and the PCB. And voila, the display was OK again.

    Some ASCII art might make things clearer, here is a side view of the LCD display:

    
              ___
             ! ! !
             ! ! !
             ! ! !
     contact !_! !
      side --> ! !
              !! !!
              !!_!!
              !___! <-- contact spring from IC socket
              !
              !
    
    

    Obviously, this probably wouldn't work on a pocket calculator because of the size of the contact springs.

    (From: Bob/Brad (santek@mb.aibn.com).)

    On some displays, the ribbon cable is fastened to the display by a heat activated adhesive, called a "heat seal" for obvious reasons. Once you take the old one off it must be replaced with a new one. In my experience you cannot try and reattach it never works. There is a special tool made for doing this (attaching cable to display) that consists of an iron with a bar on the end (like a T), once seal is lined up you press bar onto tape for a second or two and its done, but its a one shot deal. I used to do quite a few when I worked for a company that repaired pocket organizers, lots of fun!!

    Comments on soldered flex cables

    (From: Ken Bouchard (bouchard@ime.net).)

    These are the leading cause of problems for me! I repair camcorders for a living, and all too often have seen these flex cables fall off the PCB, or are so delicate in construction that they fall away from the PCB.

    In many cases during repair stage, I often touch up the soldering with a low heat iron, while pressing down on the soldered to PCB area of the cable, with a flat plastic blade, enough to re-flow the connection. Then I take and apply some general purpose glue around the cable to get it to adhere better to the PCB and prevent tearing. Of course the consumer never should encounter a problem unless the camcorder is dropped, and the case splits open and rips the connectors away from the PCB.

    Sony is infamous for having connectors fall off the boards. Many brands of camcorders are infamous for having connectors that mate 2 boards together break away from the PCB. It is a very bad situation because the boards they work with are very expensive to replace. For the cost of a simple piece of flex cable and 2 insertion force sockets, it is amazing they are cheap and choose to mate the boards together directly, knowing that failure is just around the corner!

    Most commonly the CCD board or camera assembly is mated to the video (main) PCB in this fashion and it is very sad when they break due to stress. This is one reason that the consumer should never ever attempt to repair delicate items like this.

    The best you can hope for in dealing with these is to never attempt to repair the flex cable by soldering to it, etc. That is asking for future problems at best...

    Don't 'tin' the ends of the cable either, you simply melt and distort it so that it will no longer get a good connection into the socket. Only clean it possibly with denatured alcohol if needed - otherwise replace it.

    Also do not stress them, you soon discover how easily they rip!

    About elastomer ('zebra stripe') connectors

    Remember that first (or last) digital watch you took apart? Remember how a little piece of rubber fell on the shag carpet and you thought: "What the heck, that can't be anything important". Remember how the watch's display never worked again? Well, you lost the connector that linked the LCD panel to the logic board.

    Elastomer or 'zebra stripe' connectors are used to attach LCD panels to the logic board and interconnect multiple boards on digital watches, calculators, pocket computers, and many other modern gizmos. It seems as if every cheap and many not so cheap gadgets now uses this connector technology.

    They can shift position, become dirty, and lose pressure due to warpage or damage to the plastic retainers. Very often, a weak display or missing segments can be traced to a problem with these 'zebra stripe' connectors. Equally often, disassembling, cleaning all parts with alcohol, drying, and reassembling will return the device to (better than) new condition. When installing, make sure the striped edges are against the circuit traces if there is any ambiguity.

    Of course, it isn't that the zebra stripe shifts position a small amount - by its nature this should not matter. However, if the display shifts with respect to the circuit board contacts or the zebra stripe material becomes twisted or angled, poor and/or erratic connections will result.

    (From: Spehro Pefhany (speff@gold.interlog.com).)

    These are conductive elastomer connectors made from alternating layers of conductive (carbon filled) and insulating silicone rubber.

    There are also lower resistance versions with embedded wires, but they are not used for LCD displays because the series resistance doesn't matter for LCD's.

    Alignment to the PCB is critical as is even pressure, so they tend to be used only in high volume applications where a metal stamping or plastic molding is used to hold all the parts in place.

    Identifying wiring on an auto radio/cassette

    So you want to use your old car stereo as a boombox but don't have the connection information. Here is what I would do:

    Locate the power - there will be a +12 switched and possibly a +12 unswitched for channel memory. At least one may be obvious if has an in-line fuse. Use an ohmmeter if necessary. Once you have found the power connections, power it from your 12 V power supply. Keep the volume way down and use the balance and fader controls to identify the speaker connections. There will be either 2 pairs of wires or more likely 4 pairs for front and rear speakers.

    Ray's notes on plastic part repair

    (From: Raymond Carlsen (rrcc@u.washington.edu).)

    I recently had to repair a power supply for a camcorder. It was dropped. Parts of the case were broken, and the circuit board inside was cracked. Board repair was easy. I glued the PC back together with superglue and soldered across the broken traces with jumper wires.

    The plastic case presented me with more of a challenge. Two little "ears" held the front end cap on the unit with small screws. The ears were broken into several pieces and could be heard rattling around inside the case. I could glue them back together, but the results have, in the past, been unreliable at best.

    I decided to try and reinforce the plastic. I often melt solid hookup wire across a break (on the inside, where it doesn't show) with a soldering iron to strengthen a glued area, but these tabs were so small, any heat would warp them and the case would not fit back together. What to do?

    I noticed once that when Superglue gets on ordinary notebook paper, it gets hard as a rock. It is difficult to tear, but is flexible enough to bend a little without breaking. Since one side of the little plastic ears were essentially flat, I superglued a strip of paper on each ear. The glue partially melted the plastic and made a good strong bond. After the glue set up, I trimmed the edges with an Xacto knife and poked holes in the paper for the mounting screws. The finished repair is stronger than the original product. The paper reinforcement is thin enough that there was no problem fitting the front back on the case.

    Putting equipment into long term storage (Self-Stor, etc.)

    Electronic equipment is happiest if kept in the same type of environment that humans like - moderate temperatures, low humidity. What if you are forced to store equipment for months or longer in a non-environmentally controlled space like a public storage facility?

    Recommendations:

    1. Find some long lost relatives who will store the electronics for you in a heated space.

    If this is not possible:

    1. Seal each piece of equipment in a thick plastic bag along with a pack of dessicant to keep it dry (that silica gel stuff you always throw away). This will preferably be in the original packing box (and include all cables, accessories, and manuals, so they won't get lost.)

    Moisture is more of a problem than the absolute temperature (within reason) or temperature fluctuations. Therefore, avoiding the totally damp and dingy dungeon of a medieval castle is definitely desirable.

    Dealing with a kit that was assembled by someone else a long long time ago

    When you purchase a commercial piece of equipment, it is assumed that the construction has been done properly. This may not always be the case but it is more likely when a million of something is manufactured than a hand soldered kit possibly assembled by someone who barely knew which end of the soldering iron to hold!

    I picked up a Heathkit DMM at a garage sale for next to nothing that had apparently never been quite completed. The problem turned out to be a defective rectifier in the power supply. However, everything else including the soldering was perfect. For kits, this may be the exception :-(. The original owner must have given up when the DMM didn't power up properly - and had no DMM to debug it with!

    (Portions from: jmccarty@sun1307.spd.dsccc.com (Mike McCarty)

    1. Look for improperly soldered joints. Kits often are soldered by people with, shall we say, less than completely optimal soldering skills. I have looked at kits I assembled when I was a teenager, and can't believe the joints were really that bad.

    2. Clean any switches or other moving contacts with some good TV tuner cleaner.

    3. Vacuum out any dust which may have accumulated. I prefer that to using compressed air, but you may use that also; be careful of compressed air which may come out with a high static charge.

    4. Reseat socketed components and any boards with edge connectors. If the contacts look oxidized, clean them with a soft pencil eraser and/or contact cleaner. Look for loose spade connectors as well.

    5. Check for loose screws or other fasteners and tighten if necessary.

    6. Jiggle wires and look for corrosion/fatigued wires especially where flat ribbon type cables are used

    7. Where something is more than 10 years old (in particular), it may be a good idea to check and/or just replace any electrolytic capacitors which may be drying out.

    8. Replace any primary batteries after thoroughly cleaning the battery contacts. Depending on age and previous use types may also be bad as well. Discharged lead-acid types more than a year or two old are likely hopeless. However, I have found some NiCds that were quite old and perfectly fine.

    9. Finally, if the equipment had possibly never been operational (i.e., you found the cover still in its protective plastic bag!), check ALL components for proper location and direction before applying power. Of course, it may already be too late if there was a part installed incorrectly and the original owner attempted to power it up.

    Cleaning exterior surfaces

    CAUTION: Whenever using any cleaning agent, always test it first on an inconspicuous area (rear, bottom, etc.) first to assure that there is no degradation of the base material, any protective coating, and printing/labeling. There should be *no* evidence of the color of the paint or printing showing up on the cleaning cloth, nor any change in surface texture or appearance (other than to be cleaner!). Allow adequate time for the solvent to evaporate completely before making a decision.

    I usually start with soap and water or mild detergent. If this does not work, rubbing or 91% medicinal alcohol, 'Windex', and then, WD40 are tried. All of these are usually safe for plastics though some paints or printing may be affected or completely dissolved. In particular, a fine lacquer finish may be ruined by even mild solvents including what's in Windex. Scouring powder and/or sandpaper is only used as a last resort! :-) However, in some cases, where there is serious discoloration due to heat and ozone, these may prove somewhat effective...

    One or more of the following will probably work even for tough tobacco smoke/tar buildup (also more in the next section, below). However, I cannot guarantee that some of these won't cause damage. Again, test in an inconspicuous area first!

    (From: Terry DeWick (dewickt@esper.com).)

    I have found plain household ammonia works well especially since it is cheap, if not available I use '409' or 'Fantastic' cleaners.

    (From: Ralph Wade Phillips (ralphp@gcstation.net).)

    'Scrubbing Bubbles' bathroom cleaner (Dow is the brand I use) works better than anything else I've found yet, besides chucking the case.

    Be sure to follow with a decent Windex-like cleaner - the residue from the Dow cleaner will cause you to gasp every so often for the next six months!

    (From: Joe (joeb@viaduct.custom.net).)

    Go to SAM'S and get a jug of 'ENTNT'. Mix it in a spray bottle with water (I like about one part ENTNT to four parts water) and enjoy watching the nasty brown yuck drip off the monitor. Finish the job with windex to remove the residue from the ENTNT. The ENTNT is safe on plastic, but test it on painted surfaces first.

    Eliminating tobacco smoke smell from electronic equipment

    Of course, the best way to avoid this hassle is to not subject your equipment to second-hand smoke. However, where you picked up something at a garage sale or flea market, you its previous habits may have been out of your control!

    CAUTION: Where an oven is suggested for drying, make sure it's temperature can be set low enough to avoid melting plastic and damaging sensitive electronic components!

    (From: Hapticz (hapticz@email.msn.com).)

    First, unplug it. then open it up as much as possible. get a spray bottle of Fantastic and cut the strength in half with water.

    Put the thing over the kitchen sink and spray away. let it sit for a minute and watch the yellow nicotine crud slither out. repeat if necessary you shouldn't even have to do any scrubbing.

    Avoid getting the stuff into inaccessible dial spaces, water spots are inevitable.

    Then, and this is very important, use the sink spray to thoroughly, very thoroughly, rinse any hint of cleaner out. (it is NaOH, most all cleaners are)

    Shake it off, spin it around, whatever, to remove excess water.

    Heat your oven to 140 degrees F. put in oven for 2 to 3 hours. use some kind of metal cookie sheet between it and the oven elements to avoid radiant melting.

    If it's got a lot of plastic, lower the heat to 120 and leave for 4 to 5 hours.

    Hair dryers work well if you're willing to stand around for 2 hours.

    It sounds weird, but it has worked very well for me on many items.

    (From: Jerry Greeberg (jerryg50@hotmail.com).)

    In the high end service industry boards are washed when serviced if the need arises.

    You can use a mild soap. At home Fantastic will do the job for getting rid of cigarette stains and grimy dirt on boards. You will have to rinse them very well with water afterwords.

    You can dry your boards in an oven at about 120 to 150 degrees F. But your home oven may be a bit too intense for this. The upper element tends to come on too strong at times because your oven was really made to work much higher.

    You can shake off the boards and let them dry under some 60 watt lamps for a few days. Make sure they are not too hot on the boards. Do not exceed about 160 degrees F. average, or you can cause some damage.

    It is very important that you let these boards be properly dried before putting the power back on them.

    As for the case and non electronic pieces, you can also wash these... These must also be very dry before assembling. A drop of water on the electronics will cause you a lot of grief, and possible damage, if the power is turned on with wetness present.

    I would say that you can do a mild cleanup by just blowing the boards off with forced air, and then gently cleaning things with Q-Tips, paper towels, and isopropyl alcohol.

    It is extremely important that you do not disturb any trimmer adjustments, or devices that effect the alignment of the boards. you will never be able to get these adjustments back to their proper positions yourself without the proper test gear and facility setup.

    You can take the case apart and wash all the non electrical parts with dish soap and water. Also these parts must be properly dried before assembling.

    (From: John (jberenyi@tacisp.com).)

    Well I tried it. Took the radio completely apart and soaked the boards with Scrubbing Bubble foam spray. Wow does it make aluminum shine and strip that nasty crap off the boards. A final clean with Windex and a clean rinse with distilled water is the final touch. Then I used compressed air to get most of the water removed. Next I got a cardboard box to put all the equipment in to and hooked up a 100 watt bulb and thermometer. I baked everything for 2 days at 130 degrees. Sure looks nice and works great!

    When glue is more than glue

    (From: Jim Leone (jim.leone@paonline.com).)

    I have two words (no they are not plastics --- sam): Resistor Glue.

    A lot of today's electronics manufacturers, before the printed circuit board goes through the flow solder machine, use a certain type of glue to hold down large components like heatsinks, electrolytic capacitors, and resistors. After 2 to 3+ years of life, bonded to a high temperature component, this glue turns conductive!!!!!!!

    One blatant example of this is the Viewsonic (however many other manufacturers use the same type of stuff) 4e Model 7033 computer monitor where the 86VDC main rectifier on the switching supply has it's pins coated with this 'Resistor Glue'. When the monitor was new the glue has a tan color and kind of feels like really dried up chewing gum. You know, the kind that has been under a desk for 1 year. After about 2 years, the color has changed to a darker brown; it could be almond to dark walnut colored. Now you should be able to easily remove it by scraping it away with an Xacto knife, and it will crumble away.

    However, in equipment left on 24 hours a day in moderate to high heat environments this glue takes on a more carbon hue. Typical units have holes burned right through the circuit board and others are left with carbon scarred 'divits' on the board that must be gouged out to keep the supply from arcing across.

    On one hand, an optimist might say that this is a result of engineers who's goal was to get the product out before the deadline at the end of the month.

    But on the other hand, a pessimist could say that this is a result of blatant planned obsolescence

    Grounding of computer equipment:

    While electronic equipment with 3 prong plugs will generally operate properly without an earth ground (you know, using those 3-2 prong adapters without attaching the ground wire/lug), there are 3 reasons why this is a bad idea:

    1. Safety. The metal cases of computer equipment should be grounded so that it will trip a breaker or GFCI should an internal power supply short occur.

      The result can be a serious risk of shock that will go undetected until the wrong set of circumstances occur.

    2. Line noise suppression. There are RLC filters in the power supplies of computer and peripheral equipment which bypass power supply noise to ground. Without a proper ground, these are largely ineffective.

      The result may be an increased number of crashes and lockups or just plain erratic wierd behavior.

    3. Effectiveness of surge suppressors. There are surge suppression components inside PC power supplies and surge suppression outlet strips. Without a proper ground, H-G and N-G surge protection devices are not effective.

      The result may be increased hard failures due to line spikes and overvoltage events.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Specific Problems and Repairs

    Classic ATT Touch Tone phone will not dial properly

    Most electronic equipment over 20 years old would be history but many of these are still around and in service for a couple good reasons: They are very reliable, almost indestructible, and still have a solid feel rarely duplicated in modern phones. Typical symptoms are: Everything works fine except erratic or no dialing. For some buttons, dial tone would not go away. For others, tones would be accepted but will be erratic and result in incorrect digits. Certain digits may sound weak, wavery, or single frequency (rather than the proper DTMF dual tones).

    (Note that this is not the same as the situation where the phone does not dial at all - there are no tones of any kind generated. In this case, the wires to the phone may simply be reversed - old ATT touch tone phones will not dial out if they are but will work in all other respects. Modern phones generally don't care about phone line polarity.)

    While the internal wiring of these old phones is intimidating, the basic tone dialing circuitry is an amazing example of simplicity. About the only things that fail yet still permit some tone generation are the pot core coils that determine tone frequency. Therefore, this is the first thing to check.

    There are two cores which each consist of two halves glued together. Breaks seem to be a common problem due to both the age and the brittle cement used on some revs of this model phone, and probably, as a result of rough treatment when hanging up the handset, or dropping or throwing of the desk phone.

    These cores must be aligned before being glued back together. In addition, there is an adjustment plug which may need to be tweaked. I align by ear as follows: Put a known good tone dialing phone and the bad phone on the same phone line. Momentarily depress the hook switches to silence the dial tone. You will now have about 25 seconds before the nice polite operator recording tells you how to make a call. Depending on which core is bad, depress either an entire (same) row or column of buttons on both phones. (Adhesive tape is handy to hold down the buttons unless you have four hands.) By depressing the entire set of buttons, you are disabling the other tone generator so you hear a pure tone. Without turning the fine adjustment plug (assuming it was not disturbed; if it was, set it mid-range or the same as the one in the other core), rotate the loose core top until a zero beat is obtained. As your rotate the core, you will hear the pitch change. As it approaches the correct setting, you will hear the tones beat against each other. When you are set correctly, the pitches will be equal and the beat frequency will go to zero. Mark the position of the core with a pen or pencil and then glue with Epoxy or other general purpose adhesive (around the outside - not on the mating surfaces as this will affect the tone frequencies). After the glue sets, confirm and adjust the plug core if needed. These cores use a strange triangular core tool - I made mine by filing down an aluminum roofing nail (do not use a ferrous material).

    These classic ATT Touch Tone phones are virtually indestructible. However, broken cores (or actually, just broken joints on the cores) are common but easily repaired once you know what to look for. Setting the tones by referencing a known good phone seems to be a very reliable technique as the zero beat permits an adjustment to better than .1%. Note that if the reference phone is a more modern (and flimsy digital one), then pushing multiple buttons may not work as it does with the old analog models. Setting the frequency using the normal dual tones will work - it is just not as easy.

    ATT classic dial phone will not dial

    I know, you haven't seen one of these in years, but I just had to throw this in.

    Most likely it was dropped - these phones simply do not seem to fail any other way. When dropped, assuming there is no obvious damage, a little plastic stop inside the dial mechanism which is on a pivot flips the wrong way. This normally prevents dialing pulses from being generated when the dial returns to its home position but when flipped, prevents dialing totally. It is real easy to flip it back into place.

    About those old battlewagon phones

    (From: Author Unknown)

    I got a hold of a couple of old rotary dial AT&T 500 sets with the old non-modular cords for both the coiled cord and wall cord. Man, I love these old clunkers because no one likes to steal them and they last just about forever. The reason they work well is that where I put them the people mostly just answer the phone so the dial doesn't make any diff. And since they are so big and clunky they tend to stay in one place.

    I took the wall cord off and cut a hole in the back for the modular jack that I got over at Fry's for under a buck. They make it a whole lot easier to change the cord. But I haven't been able to find the same kind of jack for the four pin coiled handset cord. I also got some of the rubber ducky shoulder rest thingies over at Radio Shock, and before I put them on I decided to clean off the handle of the handset with rubbing alcohol. Man was I in for a surprise.

    I started rubbing on the handle with a cotton ball and some alcohol, and all the paint started coming off. What a MESS. After I used a lot of cotton balls and rubbing alcohol on the whole handset, I got off most of the paint, but the screw on covers for the receiver and transmitters were different colors than the original beige, one was PINK! Weird. So now I have an even uglier rainbow phone! Cleanest phone in the neighborhood, though.

    One of the phones looked like someone dropped something really heavy on it and the dial was loose from the base. So I had to drill out the rivets on the base and replace them with screws. Feels a whole lot better now. On another 2500 set, I had to take the touch tone pad apart and go in the bathroom and wash out all the dried up coke sugar goop that was in it, so now the buttons don't stick anymore. I had to take the keys out, but I couldn't remember which side the * and # went, so I had to cheat and peek at another phone. I also found out that the weird screws that hold the base to the cover are some odd screw thread like a #7 - 18 tpi.

    One interesting thing is that the 500 and 2500 sets are made to compensate for the loop length. They have varistors inside, and they do a decent job. But it seems to me that the newer electronic phones don't do such a good job of this.

    One thing I thought was really strange was the sticker on the bottom of the 2500 set. This is a AT&T 2500MMG set, and the sticker on the bottom says:

    "WARNING: USE FOR BUSINESS SYSTEMS ONLY OR YOU RISK AN ELECTRICAL SHORT CIRCUIT"

    I kind of think this is a put-on, since the phone works okay on a POTS line.

    Jerrold 400 Cable Converter Problems

    The following may also apply to other models of similar vintage (e..g, 440).

    The most common symptoms for these cable boxes relate to their not staying on or acting erratically when the buttons are pressed. The causes are usually quite simple:

    1. Cold solder joints around the power supply regulator ICs (on chassis heat sink).

    2. Dried up main filter capacitors - two large electrolytics in power supply on main board.

    Be careful disassembling the main board from the chassis as at least one of the regulator ICs clipped to the side of the chassis is insulated from this heatsink and the insulation is easily damaged.

    One cause of a totally dead converter is a blown thermal fuse in the primary of the power transformer. It will be buried under the outer wrap inside the transformer, between the bobbin and core, or molded into the bobbin, but may be repairable. Test by jumpering around it. But for safety, install a replacement.

    Original Nintendo console erratic or dead

    While the original Nintendo game machine is a couple of generations out of date, many are still in use. And, hey, kids usually don't care.

    The most common problem with these units is a worn or dirty cartridge connector. In this case, the red power/status light will continue to flash even after the RESET button is pressed with a game cartridge in place. Replacements are available for about $9 from the sources listed at the end of this document.

    First, try another game cartridge - the one that is not working may just have dirty contacts or may be defective. Clean the contacts with a Qtip moistened with water followed by isopropyl alcohol. (The water will remove the sugar from the candy that may have made its way onto the connector.)

    To get inside, you first remove the 6 screws on the bottom and then about 12 screws which fasten the circuit board and shield to the bottom of the case. (Note: there are two screws which are longer and silver colored - make sure they get back to their original location when you put everything back together.) Once all these screws are removed, the black connector can be slid off the edge finger on the circuit board Inspect these connections - they just may be a bit corroded or dirty. Use contact cleaner and/or a pencil eraser and see if that makes any difference. Use contact cleaner on the dual rows of fingers that connect to the game cartridge as well. A dental pick can be used to gently spread the fingers apart ever so slightly and thus improve the connection when the cartridge is inserted.

    Even if this only makes a slight improvement - you can press down on the cartridge and the machine will respond to the RESET button - you have confirmed that the connector is indeed the problem. In many cases, just this cleaning will result in reliable operation for a long time to come.

    Replacement connectors are under $10 from places like MCM Electronics and Dalbani.

    Repairing Texas Instruments TI-5X calculators

    I have them up through TI-57 so I don't know if the following applies to models higher than this (TI-58 and TI-59).

    If it hasn't been used for a while (like 15 years?) then the NiCds are likely deader than a door nail and will not accept a charge since they are totally shorted. Bad NiCds is very likely all that is wrong with the calculator.

    If your calculator has a pack that plugs in inside the back with 2 AA NiCds and some circuitry, then it is the same.

    First crack open the pack by using a butter knife or similar instrument at the catches along the seam. You will see a pair of AA NiCds and a small circuit board. This is a DC-DC convertor which boosts the 2.4 V of the NiCds to about 10 V to operate the logic of the calculator.

    Inspect the circuit board for corrosion and other obvious damage. Unless the calculator was stored in a damp area, it should be fine. The batteries will probably have crusty white stuff on the positive ends. They are bad. Don't even bother trying to zap them.

    As a test, you can do either or both of the following:

    1. Get a large electrolytic capacitor (e.g., 10,000 uF at 10 V) and put it in in place of the batteries. Observe polarity. Try out the calculator using the TI charger/adapter. Operations will be a bit flaky but should basically work (the capacitor, no matter how large, apparently will not substitute for the NiCds).

    2. Unplug the TI battery pack and set it aside. Find a 9 V power supply or a 9V battery. Connect this to the red and black wires coming from the logic board connector which went to the battery pack. NOTE: the wire color coding is backwards on at least some of these. Black is positive for some reason. However, nothing disasterous happens if you connect it backwards as far as I can tell since I was testing it backwards for quite a while until I caught on. And, I thought TI was a real company!

    If these tests are successful, the calculator is likely fine and you just need a new set of AA NiCds with solder tabs to make it as good as new.

    Or, if you don't need the authenticity of a genuine TI form-and-function rechargeable battery pack, use a 9V AC adapter, 9V Alkaline, or 9V NiCd battery and charge it externally.

    Some information (with photos) on battery packs for various TI calculators can be found at Datamath.org - Battery Packs. You'll find what you just read there as well. :)

    Northgate (and clone) PC keyboards

    If you've grown up thinking Dell and other mushy modern keyboards are all there ever was, there is no need to read further in this section. You've never experienced the pleasure of using a REAL keyboard with keys that have a satisfying feel and actual mechanical click. (Not to mention that the "Ctrl" key is in the proper place!)

    Northgate was a company that manufactured decent PCs in the 1980s before Gateway and long long before Dell. Their PCs had good performance, were reliable, and solidly constructed. However, one distinctive feature was the high quality keyboard. Used Northgate keyboards can still be had on eBay in the $30 to $50 range. Imagine paying that much for a 15+ year old keyboard! There are also people who will clean and repair your Northgate keyboard for a basic charge more than this - which is a testament to how attached some people (including myself) have grown to them.

    There were several models of genuine Northgate keyboards, as well as clones which used the same key switches and were nearly as good in other respects. I'm using one now and would not want to give it up! I have more than a half dozen of both genuine and clone Northgate keyboards. Aside from minor differences in the layout and extra keys here and there and features that most people have no idea of anyhow, there is little difference between genuine and clone KBs.

    (Note that since these are pre-ATX or whatever, they have the large 5 pin AT KB connector. So an adapter is needed for the PS2 connector found on all modern PCs. I also had one situation where a Northgate clone would cause an AMD-based PC to crash intermittently, reason unknown.)

    Unlike modern junk keyboards that are strictly throwaway items, everything in a Northgate (or clone) KB is easily replaceable. The electronics doesn't go bad but I have found individual key switches to become flaky or non-functional. Although new replacements may be available (I have no idea), the easiest repair is to swap the bad key switch with one from a position that is rarely used. For example, over the years I've had the "R", "C", and "O" keys go bad. I typically swap them with the "Pause" or "Scroll Lock" keys. What are those for anyhow? :) It's also possible to disassemble, clean, and repair the key switches themselves. Another common problem is that the main "Enter" key becomes sticky. This is a mechanical issue with wear of the plastic parts but the repair is basically the same (swap from a nother position), though trickier because of the additional linkages for the large key.

    So, instead of paying someone $55 or more (plus shipping) to clean your keyboard and replace a key switch or two, do it yourself. You'll need a low power soldering iron simple desoldering tool like a solder sucker ("SoldaPullet") or desoldering copper braid ("Solder Wick"), and a medium size Philips screwdriver. A multimeter is desirable to test the key switches.

    1. Before unplugging the keyboard, identify all the flaky or non-functional keys. Then unplug it. Everything can be done with no power applied. Decide which little-used keys will used as organ donors.

    2. Remove 6 Philips screws to allow the bottom cover to be removed. On some models, this is as much disassembly as required to get to the solder-side of the PCB. On others, only the top cover comes off and an additional 4 screws need to be removed holding the guts in place.

    3. Use a clean paint brush or soft tooth brush to clean out all the dust, dirt, dead bugs, dried beans, and whatever else has accumulated over the years. There will probably be some rust on the genuine metal cover from spilled soda but that has no effect on performance.

    4. Each key switch has two solder connections. A multimeter on the ohms range can be used to confirm that the switch is indeed flaky.

    5. Use your soldering iron and desoldering tool to free these terminals on each of the bad key switches. If swapping in from other positions, do the same for those.

    6. Use a pair of needlenose pliers to push the pins through the PCB. Doing so will cause the entire key switch to pop out of the plastic frame in which it is mounted. It can also be gently pried from the top.

    7. To clean and repair the key switch itself (if desired): Separate the top and bottom parts by gently pulling the two locking tabs on one side. Inside is a coil spring, a thin steel spring plate on one side, and the actual switch assembly with its own thin steel spring plate on the other. Use contact cleaner on the switch assembly. Bending the fingers a bit on the latter thin steel plate may be all that's needed to assure reliable contact. Reassemble in reverse order and test with your multimeter.

    8. Make sure the pins are straight and then push the key switch in until it seats in place. Solder the pins.

    9. Reassemble in reverse order and enjoy!



  • Back to Audio and Misc Repair FAQ Table of Contents.

    Service Information

    Determining belt type and size

    Belts are normally specified by their cross section - square, flat, round, and their inside circumference (IC). The IC is used since it is virtually impossible to accurately measure the diameter of a belt.

    Assuming you cannot locate an actual part number, determine the type of belt; square, flat, or round. If you do not have the old belt, this is usually obvious from the pulleys. Most small belts (as opposed to V-belts on 1 HP shop motors!) used in consumer electronic equipment are of square cross section though flat types are sometimes found in the main drives of VCRs, cassette/tape decks, and turntables (remember those?). Measure or estimate the thickness.

    The IC is always specified with the belt fully relaxed. This can be measured by hooking the old belt on one end of a ruler and pulling it just tight enough so that it more or less flattens out. Read off the length, then double it for the IC. Get a new belt that is 5% or so smaller to account for the old one be somewhat stretched out. Of course, if the belt broke, measurement is real easy. Or, if you do not care about the old belt, just cut it and measure the total length.

    If the old belt decomposed into a slimy glob of jellatinous black goop or is missing, you will need to use a string or fine wire around the appropriate pulleys to determine the IC. Reduce this by 10-25% for the replacement. Very often the match does not need to be exact in either thickness or length - particularly for long thin belts. A common rubber band may in fact work just as well for something like a tape counter!

    However, there are cases where an exact match is critical - some VCRs and belt driven turntables or tape decks do require an exact replacement for certain drive belts but this is rare.

    Some parts suppliers make determining replacement belts very easy with the PRB system in which the part number fully codes the shape, size, and thickness.

    Making custom length rubber belts

    The following will probably work for most drive belts except for those which are critical for accurate speed control in devices like cassette decks and turntables.

    (From: Melissa & Jim (mgkepner@facstaff.wisc.edu).)

    3M and Eastman make cyanoacrylate adhesives (super glue) that are specially made for making custom O-rings from linear stock. This seems to be exactly the same problem you are approaching. These glues work very well and produce a joint as strong as the base material, but without the need for the needle and thread. The joint can be made almost invisible. The only hard part is holding the pieces aligned while the glue cures, but in this case that is only seconds.

    I have used a machinists steel V-block for this, but one of the O-ring manufacturers sells a plastic tool for exactly this purpose. In the US, I would check at a bearing supply house; they often carry O-ring supplies as well.

    Rubber or elastic bands as drive belts?

    It is 3 AM, you have finally removed the last of the 38 screws to access the tape transport in your Suprex Never-Forget model X4123 answering machine and what do you fine? A broken belt, of course! What to do?

    As a test at least, a common elastic band may work. The recordings will likely have terrible wow and flutter but this will at least confirm that there is nothing else broken. In a pinch, this free solution can be left in place until a proper replacement arrives. This should work for many types of devices - CD players, VCRs, tape decks, etc. - where grooved pulleys are used and the belt is not called on to provide a great deal of power.

    Identifying and replacing SMT devices

    See the document: Surface Mount (SMD) Transistor/Diode Cross-reference. If this does not list your device or it is so fried that no markings survive, you can usually use some educated guesswork to select a suitable replacement. SMD types can usually be replaced with normal devices since there is usually sufficient space. If there are any other SMD parts with the identical marking, you should be able to determine pinout (e.g., BCE for transistors - see the document: Basic Testing of Semiconductor Devices) and replace with a general purpose non-SMD type. I doubt that the specifications of parts used in telephones or modems are critical. Even if there are no identical device, if you can determine the voltages on the pins, you may be able to guess the type. The worst that will likely happen if you are wrong is to blow your replacement device - anything that this will do the rest of the circuitry has already been done.

    Interchangeability of components

    The question often arises: If I cannot obtain an exact replacement or if I have a VCR, tape deck, or other equipment carcass gathering dust, or I just have some extra parts left over from a previous project, can I substitute a part that is not a precise match? Sometimes, this is simply desired to confirm a diagnosis and avoid the risk of ordering an expensive replacement and/or having to wait until it arrives.

    For safety related items, the answer is generally NO - an exact replacement part is needed to maintain the specifications within acceptable limits with respect to line isolation, X-ray protection and to minimize fire hazards. However, these components are not very common in audio equipment or other consumer devices (other than TVs, monitors, and microwave ovens) except for possibly in their power supply.

    For other components, whether a not quite identical substitute will work reliably or at all depends on many factors. Some designs are so carefully optimized for a particular part's specifications that an identical replacement is the way to return performance to factory new levels.

    Here are some guidelines:

    1. Fuses - exact same current rating and at least equal voltage rating. I have often soldered a normal 3AG size fuse onto a smaller blown 20 mm long fuse as a substitute. Also, they should be the same type - slow blow only if originally specified. A fuse with a faster response time may be used but it may blow when no faults actually exist.

    2. Resistors, capacitors, inductors, diodes, switches, trimpots, lamps and LEDs, and other common parts - except for those specifically marked as safety-critical - substitution as long as the replacement part fits and specifications are met should be fine. It is best to use the same type - metal film resistor, for example. But for testing, even this is not a hard and fast rule and a carbon resistor should work just fine.

    3. Potentiometers - user knobs usually control one or more of these. There are four considerations in locating a suitable replacement: resistance, and taper, power rating, configuration, and mechanical fit. Configuration refers to the number of ganged pots, concentric knobs, etc. Matching this from your junk box may prove to be the toughest challenge! Many of the controls for audio equipment use what is known as an 'audio taper'. This means that the resistance change with knob rotation is not linear but is designed to produce a uniform incremental change in perceived volume, for example. Replacement with a linear taper pot will squish all of the effect towards one end of the range but it will still work. If measuring the resistance of a (good) potentiometer with its wiper set in the middle results in significantly different readings from center to each end, it is most likely an audio taper pot (though some other weird taper or other peculiarity is possible).

    4. Rectifiers - many are of these are high efficiency and/or fast recovery types. Replacements should have equal or better PRV, If, and Tr specifications. For line rectifiers, 1N400x types can usually be used.

    5. Transistors and thyristors (except power supply choppers) - substitutes will generally work as long as their specifications meet or exceed those of the original. For testing, it is usually ok to use types that do not quite meet all of these as long as the breakdown voltage and maximum current ratings are not exceeded. However, performance may not be quite as good. For power types, make sure to use a heatsink.

    6. Switching power supply transistors - exact replacement is generally best but switchmode transistors that have specifications that are at least as good will work in many cases. See the documents: "Notes on the Troubleshooting and Repair of Television Sets", "Notes on the Troubleshooting and Repair of Computer and Video Monitors", and "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies" for more info.

    7. Audio and erase heads - may be possible if the mountings are reasonably compatible. However, there could be other unknowns like coil impedance and drive requirements. The connectors are not likely to be similar either. There are usually significant differences in head configuration and mounting arrangement between 2 head, 3 head, and autoreverse cassette or open reel tape decks.

    8. Motors - small PM motors may be substituted if they fit physically. Make sure you install for the correct direction of rotation (determined by polarity). Capstan motors - especially the direct drive type - are probably not interchangeable. However, generic speed regulated cassette drive motors are available.

    9. Sensors - many are sufficiently similar to permit substitution.

    10. Power transformers - in some cases, these may be sufficiently similar that a substitute will work. However, make sure you test for compatible output voltages to avoid damage to the regulator(s) and rest of the circuitry. Transformer current ratings as well as the current requirements of the equipment are often unknown, however.

    11. Belts, tires, and pinch rollers - a close match may be good enough at least to confirm a problem or to use until the replacements arrives.

    12. Mechanical parts like screws, flat and split washers, C- and E-clips, and springs - these can often be salvaged from another unit.

    The following are usually custom parts and substitution of something from your junk box is unlikely to be successful even for testing: SMPS (power supply) transformers, interstage coils or transformers, microcontrollers, other custom programmed chips, display modules, and entire power supplies unless identical.

    Why are there parts missing from my equipment?

    It is not uncommon for parts to be missing from production equipment due to design changes or field mods. Thus, it may not mean anything. Inspect the solder pads - if they look the same as all the others, it was probably never installed in the first place. Of course, that could have been a manufacturing omission as well. Parts just don' jump ship without leaving evidence behind!

    Don't be tempted to add a part just because there is an empty spot. In some cases, like the RCA TV that would tend to blow HOTs if the power failed, that would be a really bad idea and complicate your troubleshooting.

    Whole blocks of circuitry are often left unpopulated on lower priced models. You didn't pay for those features. Sometimes, this can work to your advantage enabling you to upgrade to a fancier model for the cost of the parts.

    Some general references

    Here are some suggested titles that might be found in your local public library or a technical bookstore.

    1. Troubleshooting and Repairing Electronic Circuits
      Robert L. Goodman
      Second Edition
      TAB Books, Inc., 1990
      Blue Ridge Summit, PA 17294-0214

    2. Small Electric Motors
      Rex Miller and Mark Richard Miller
      Second Edition, 1992
      MacMillan Publishing Company
      866 Third Avenue
      New York, NY 10022

    3. Repairing Quartz Watches
      Henry B. Fried
      American Watchmakers Institute Press, 1988
      Cincinati, OH
      ISBN 0-918845-06-8

    4. Readers Digest Fix It Yourself Manual
      The Readers Digest Association, 1996
      Pleasantville, New York/Montreal
      ISBN 0-89577-871-8

    5. The Complete Guide to Digital Audio Tape Recorders including Troubleshooting TIps
      Erik S. Schetina
      P.T.R. Prentice Hall,
      Englewood Cliffs, NJ 07632
      ISBN 0-13-213448-9

    6. DAT - The Complete Guide to Digital Audio Tape
      Delton T. Horn
      TAB Books, Inc., 1991
      Blue Ridge Summit, PA 17294-0214
      ISBN 0-8306-7670-8 (hardcover), ISBN 0-8306-3670-6 (paperback)

    7. Troubleshooting and Repairing FAX Machines
      Gordon McComb
      Tab Books, a division of McGraw-Hill, Inc., 1992
      Blue Ridge Summit, PA 17214
      ISBN 0-8306-7778-X (hardcover), 0-8306-3778-8 (paperback)

    8. Complete Guide to Home Entertainment Equipment - Troubleshooting and Repair
      John D. Lenk
      Prentice Hall, Inc., a division of Simon and Schuster, 1989
      ISBN 0-13-161001-5

    9. Understanding Telephone Electronics
      Fike and Friend

    10. Installing Telephones
      Radio Shack
      Catalog number: 62-1060

    11. All Thumbs Guide to Telephones and Answering Machines
      Gene B. Williams
      TAB Books, Inc., 1993
      Blue Ridge Summit, PA 17294-0214
      ISBN 0-8306-4435-0 (paperback)

      This one is very basic but does cover the most common problems and has illustrated instructions for general telephone wiring, adding extensions, answering machine cleaning, rubber parts, simple electronic problems, etc.

    And, for that older audio equipment (including record changers):

    1. Repairing Home Audio Systems
      E. Eugene Eckland
      McGraw-Hill Book Company, 1962
      Library of congress catalog number: 61-18021

    Recommended parts suppliers

    For general electronic components like resistors and capacitors, most electronics distributors will have a sufficient variety at reasonable cost. Even Radio Shack can be considered in a pinch.

    However, for consumer electronic equipment repairs, places like Digikey, Allied, and Newark do not have the a variety of Japanese semiconductors like ICs and transistors or any components like tape heads or belts.

    See the document: Major Service Parts Suppliers for some companies that I have used in the past and others that have been recommended. Also see the documents: Troubleshooting of Consumer Electronic Equipment.



  • Back to Audio and Misc Repair FAQ Table of Contents.

    -- end V3.50 --