[757labs] 37" TV, power supply troubleshooting
kludge at panix.com
Wed Jun 22 08:21:32 EDT 2011
Indeed. Look inside the power supply; most of them have a single-chip
controller like the UC3842. Look at that chip; it will have two or more
inputs for it to receive current and voltage information, and it will shut
itself down if they are out of range for a second or so after startup.
Use a scope to look at those pins; they move too fast to use a DVM. You
can kind of eyeball the voltages with a Simpson 260 if you're careful but
a scope is much better.
One of them will be out of range. And I agree, it will probably be out of
range because the output of one of the supplies is being pulled down to
ground by a failed capacitor.
The ESR meter is an absolute and utter miracle for finding bad electrolytics
in a string. I have the cheap Dick Smith one and aside from the fact that
it runs the battery down when it's not in use, it's been the greatest time
saver on the bench.
But, a good argument can be made, if you're intending on keeping the thing for
a long time, that you should just shotgun all the damn things out and replace
them all with Panasonic FM or EB types from Digi-Key.
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