These are the little gadgets and homemade testers that are useful for many
repair situations. Here are just a few of the most basic:
|NotTaR of Television Sets : Incredibly Handy widgets
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- Series light bulb for current limiting during the testing of TVs,
monitors, switching power supplies, audio power amplifiers, etc. I built
a dual outlet box with the outlets wired in series so that a lamp
can be plugged into one outlet and the device under test into the other.
For added versatility, add a regular outlet and 'kill' switch using a
quad box instead. The use of a series load will prevent your expensive
replacement part like a horizontal output transistor from blowing if
there is still some fault in the circuit you have failed to locate.
- A Variac. It doesn't need to be large - a 2 A Variac mounted with
a switch, outlet and fuse will suffice for most tasks. However,
a 5 amp or larger Variac is desirable. If you will be troubleshooting
220 VAC equipment in the US, there are Variacs that will output 0-240 VAC
from a 115 VAC line (just make sure you don't forget that this can easily
fry your 115 VAC equipment.) By varying the line voltage, not only can
you bring up a newly repaired TV gradually to make sure there are no
problems but you can also evaluate behavior at low and high line voltage.
This can greatly aid in troubleshooting power supply problems. Warning: a
Variac is not an isolation transformer and does not help with respect
to safety. You need an isolation transformer as well.
- Isolation transformer. This is very important for safely working on
live chassis equipment. Since all modern TVs use a line connected power
supply, it is essential. You can build one from a pair of similar
power transformers back-to-back (with their highest rated secondaries
connected together. I built mine from a couple of similar old
tube type TV power transformers mounted on a board with an outlet box
including a fuse. Their high voltage windings were connected together.
The unused low voltage windings can be put in series with the primary
or output windings to adjust voltage. Alternatively, commercial line
isolation transformers suitable for TV troubleshooting are available
for less than $100 - well worth every penny.
- Variable isolation transformer. You don't need to buy a fancy combination
unit. A Variac can be followed by a normal isolation transformer. (The
opposite order also works. There may be some subtle differences in
CAUTION: Keep any large transformer of this type well away from your monitor
or TV. The magnetic field it produces may cause the picture to wiggle or the
colors to become messed up - and you to think there is an additional problem!
- Degaussing coil. Make or buy. The internal degaussing coil salvaged
from a defunct TV doubled over to half it original diameter to increase
its strength in series with a 200 W light bulb for current limiting will
work just fine. Or, buy one from a place like MCM Electronics - about
$15 for one suitable for all but the largest TVs. Also, see the section:
Degaussing (demagnetizing) a CRT.
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