Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old May 19th 05, 02:48 AM
dougk_ff7
 
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Default Sony TV-- KV-1913 (SCC-265B-A) Power Supply Issue?

I've been working with a dead Sony KV-1913 for a while... apparently,
all of a sudden, it started making all sorts of buzzing noises, and
just failed to work. From a friend's advice, I checked capacitors,
replaced one, and at the same time, replaced a blown 1.5A fuse (like it
just popped of old age... no blackening around the glass). So all is
well, I go to power it up, and apparently, something else isn't quite
right--it blew its main 5A fuse pretty fast. Tried bringing it up in
series with a light bulb (with the degauss coil removed), and the light
bulb is almost at full brightness, probably indicating a short, though
resistors and capacitors seem to check out fine in the power supply
section. Also, when powered on with the light bulb load, there is a
high-pitched whine (perhaps the horizontal deflection?) Transistors
were also checked, and I didn't see any giving a dead short, but I
might be missing some...

Pretty much, if this is the flyback giving me headaches, I think it's
time to retire this TV and take it out to the recycling center, but if
it's possible it is another part that I haven't checked, or perhaps
missed, help would be appreciated. I've tried running through all of
the possible scenarios on the SER FAQ, and just haven't made it any
progress with any of those possibilities...

Perhaps one source of this short, the only place on the board I noticed
blackening was in an insulated clear tube--I think it's insulating a
capacitor in an odd spot beside all the connectors (to the power
switch, degauss, etc.) and near the main filter capacitor. It seems to
be charging up fine, but that's the only spot I see any blackening at
all.


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Old May 19th 05, 02:56 AM
dougk_ff7
 
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I will ammend this--it seems there was some other arcing that I missed,
around NL601 (the side of the gray rectangular container is lightly
blackened and there's a nearby connector that seems to be blackened
slightly as well... hmmm, schematic would be useful here. Tempted to
get the Sams' Photofact, but for $20 for something I probably won't use
very much (and for such an old TV), might not be worth it.

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Old May 19th 05, 03:21 AM
 
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dougk:
Is the HOT shorted? You will want to take it out of the circuit to
test it conclusively. Also check the flyback derived B+ loads.....
electrolytics and diodes.
electricitym

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Old May 19th 05, 05:36 AM
dougk_ff7
 
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Okay, a bit closer here. I replaced this part with an identical part
(I had another Trinitron in the basement that had a bad degauss coil...
and all the attempts to repair that were useless). Result was still a
blown fuse, although this one didn't completely obliterate itself--the
fuse kindly popped and returned to normal. No nasty blue spark or
anything from the fuse. Maybe I replaced a Slo-Blo (or even medium
response) fuse with fast-blow, or maybe I still have a short somewhere
in the line. The original fuse was a SOC ST6 (125V 5A) fuse... though
I can't find any data on this. Size seems to be a 3AG.

I'll probably give it a rest for tonight and come back to it
tomorrow... make final checks with a meter before I go and replace the
fuse with something slower-acting. At least I've made some progress. :P



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