Lexel 88 problems - Help please

[gottaluvlasers]

Steve-

you never cease to amaze me! your knowledge and expertise is simply staggering.

sorry, lol. Just thought i'd throw that in here.

-Marc

[smogthemog]

I agree Marc, it is simply astounding how Steve knows SO bloody much!

Me here - Mr seive head that forgets his own bloody name sometimes

No worries at all Steve, You are a god send!

I have another 6259 (that came out of the original PB set) with a Hfe of 30 so I will put that in the one with a reading of 4.

[mixedgas]

Um, my first 88 came out of a dead medical system in college and cost me 400$. A laserist in Hong Kong faxed me a schematic to a Kinkos fax machine on Xmas eve, God Bless Him. Then later on For four years I made part of my living keeping 5 lexel psus running single line argons and kryptons 24/7 with no dropouts and only 2-3 mode hops per 24 hours allowed. I later got to know the factory service engineers quite well. I've been known to ask questions the factory cant answer. Which is why when a friend bough part of the factory at auction, I went 700 miles and did some studying.... Rumor has it I might even have the drawings for the... um never mind.. I don't need to tick the other B.B. in the business off.

Its just a matter of time and study, and being a kid in a town with 3 of the best science libraries in the US. I was too scrawny to make the teams so I had to do something with my time. I would gladly trade all these "skills" to be able to play the piano, nightly, in a dimly lit bar.. Ie do a Barry Manilow... But I have zero brains or genes for music.. Or math for that matter...

If I ever make it to the UK Smog can buy me a diet soda or something... I Cant have alcohol with this BP med... unless I have a nurse or emt around, It knocks me on my a**

Steve

[shrad]

Steve,

if lasers were music, you would be Steve Vai



be sure there are plenty of people who also prefer to earn big experience instead of "going with the mass" when they are young (I'm in the same case), and finally, that experience is paying back with rewards (though I agree, not always financially)

if there was a good photonic industry in Belgium, I'd say go here and have a try, as we have one of the best health care and social system... but that's another story ^^

[smogthemog]

If you get CW tube current with no cards installed the zener is bad, is shorted or breaking down and driving the passbank early. The zener is there to turn the passbank on a bit to pass the ignite pulses and protect the transistors. But if your getting lasing with no cards and no shorted transistors, its the zener turning on, or in rare cases one of the two drivers is bad. Its OK to lift one leg of the zener for a few starts with the cards out.
Steve

I have replaced ALL the transistors on the PB now but am wondering what Zener you refer too above Steve? Is it the 5W 60v one?

Can I now do the 12v test on the PB Steve? Is there anything else I need to take into consideration?

Jim

[mixedgas]

yes, you want to look at the 60V zener. When it fails, it latches the passbank on. Yes, you can do the 12V passbank test. This is NOT a normal procedure except for a catastrophic failure. I don't want everyone who stumbles across this thread to think that appling a big PSU is the normal way to test a passbank. It is NOT. But in your case its a welcome help if you can current limit your load, ie resistor, lamp, or adjustable current limited psu and keep it to a few amps. And you have the skills to do it, most don't. The Cr52 passbank is very similar to the Lexel. Again, unless its a major rebuild, a ohm meter suffices to do a Lexel passbank. Remember, in your case, you'll need a potentiometer to bias the driver base on, gently

John Rucbacha keeps the cr52/cr54 manual on his website. Details are in there. There are simularities.

read here:

http://www.jklasers.com/cr54laser/cr54laser.htm

Keep us informed. Steve

[mixedgas]

Smog, check the FTP site ilda swap under smog85mog.zip

Schematics for a 85-1 scientific, an 88A is very similar except the transformer is a bit more massive. taps and some stats included.

I passworded it because of DJ Creepers, who cannot keep his mitts off da blinkenlichten. I'd love to just stick it inline in the thread, but I'm sure you'll understand. PMed you with the password.

Steve

[smogthemog]

I have tested the PB tonight Steve and AFAIAC, it seems to be working.

I put my PSU between the -HV on the Cap top and the center tap of the Filament TXFMR. I then gor a 9v battery and connected a 10K pot across it with the wiper connected to the base of the small driver TX.
All the negative where interconnected.

I then applied the 12v and slowly wound up the pot.

As you can see from the photo's, if you can be bothered to wait for the piggin things to load! , it starts to load up at 1.6v on the base. At 2.13v it is drawing 1.7A across the PB and at 2.5v it's at 3A.

Is this a good indication of it working Steve?

I have tested it up to 25V and all seemed well.


Is there any further tests I can do now with 230Vac power to the PSU with the head disconnected and the interlocks defeated?

I will be fitting the new components to the CPC and testing that later.


EDIT - CPC has all the new components fitted, Zeners, transistors & Diodes, (I have also ordered a new LM301AH Op-amp as well just in case (Shall I fit it anyway Steve??)) and I now have all voltages present and correct

[mixedgas]

Oh, you have one of those nice Circuit Specialists current limited PSUs. I have one one too.



I'd plot base voltage vs supply current reading for further use, and then do a quick check of the current flowing through each emitter by putting the voltmeter across each emitter resistor. I'd also measure base to emitter voltage and collector to emitter voltage at full current using your dc test setup.

Nice way of testing, greatly reduces explosions.

Card testing.
remove LM301.
Connect a set of test leads to circuit specialists PSU. Set PSU to max voltage. short leads. Adjust PSU constant current mode to 100 mA indicated. Unshort leads. connect ground to ground on card at pins 19 or 20. Connect B+ from PSU to Of couse with that PSU (18V version?) you may even get close to turning on the +30V or the +20V zener, but you should see the other voltages and the neg rail. adding a 9V battery in series with the PSU would get you 27V and you might see the 20V zener start to clip.
(remember this must be current limited some how) So you should see +15, some negitive voltage etc. What you get depends on how good your inverter circuit on the board works.


Things we check with head disconnected but interlock defeated and control card removed. You MUST use a floating battery powered voltmeter for these tests!!
.............
Disconnect psu from line voltage.
Set taps per chart I sent you.
CAUTION, LETHAL VOLTAGES PRESENT!
reconnect line power.
close breaker, do NOT press start,
I. confirm line neon lit.
II. Check "AC" test points with volt meter, shoud be some place between 110 and 133 volts.
IF NOT< STOP> Should be NO dc across cap. If there, is, bad contactor, stop.

Now set meter switch to reg volts

Press start.
III. Massive THUMP from contactor closing.
IV Breaker cooling fan should start and run smoothly.
V. Power neons (2) lit and stable.
VI, NO smoke.
VII cap should rapidly start to charge, with massive surge.
VIII. Low AC ripple across cap (most modern meters CAN look at AC sumperimposed on DC, use 110V ac scale, but check meter manual, may be a volt or two or three residual ac, but any massive amound of AC means BAD cap)
VIII no reg volts reading If reg volts more then just off peg from leakage, power down straight away.
VIIII switch to amps. NO amps flowing IF amps flowing power down.
X. Switch to DC volts, should match open circuit V on cap +/- 5% or so.

XI, Open circuit voltage unloaded should be around or greater then 1.414 times the AC voltage from the buck/boost autotransformer. Do note it is a autotransformer , not isolated, and may act a bit strange when unloaded.

XII cathode transformer unloaded should be in the greater then 3 volt region and the voltage should change a small amount as you change the cathode switch. Power down main breaker before changing switch.

115NO30 relay should require about 30 seconds to time in.

Pin P (anode) to either of the cathode leads should be the same as the DC cap voltage.

------------------

Thats enough for tonoght, more to follow.

Steve

[mixedgas]

If you have no way of testing a OPAMP, and you have a stereo or computer speaker around, or a scope. This circuit may be of help..
This is a simple relax oscillator, and does a OK job of testing most opamp's inputs and output. It will produce a fast square wave going both above and below zero. You can use a piezo speaker to hear the buzz, route it into a sound card or audio amplifier, or hook up a dual color or back to back led. Both leds lit or yellow if dual color means its probably oscillating. So does a lound buzzing if doing the audio route. On a scope or sound card scope, it is a bipolar square wave.

Steve

SLOPERATIONAL..bmp