"Jerry G." wrote in message ...
I would be inclined to believe that your fault is more some component(s)
became thermo sensitive. If you are prodding at the board, and there is not
intermittency, then most likely it is not a cold solder connection.

To follow this logically, you would have to use a scope while the fault is
occurring to track down where the intermittent is. Or, you can try getting
some cold spray and a heat gun, and use the technique of heating and cooling
the various components to find this.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
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Jerry,

Thanks for the suggestion. Using cold spray I isolated the
intermittency to a single transister (Q352). Just the slightest spray
on this transistor brought back the video signal.

Inspecting the solder connections of this transistor revealed cold
solder joints. However, even after reflowing the solder on the
transistor (and Q351) the same intermittency occured.

Okay, so I figured that in addition to the cold solder joints, the
transistor itself has become heat sensitive (as Jerry mentions). Q352
is marked with "B621A", but the parts counter guy cross-referenced
this part to NTE159 (instead of NTE294). Installing the NTE159 part
did not improve the situation, in fact, a video signal never appeared
at the output :-(

No parts dealer in town (that is open today) has an NTE294 in stock,
but one shop had a 2SB544 in stock, which also cross-references to
NT294. Hmm... perhaps the 2SB544 will work. Installing the 2SB544
had the same results as with the NTE159, i.e. no video signal at all.

I now realize that simply because 2 parts cross-reference to the same
part (NTE294 in this case), that the 2 parts themselves may not be
interchangable since the maximum ratings may be significantly
different. Live and learn.

Anyways, I'm wondering if any other component(s) may have been damaged
due to my experimentation, particularly Q351 (D592A). I'm guessing
that Q351 and Q352 form a push-pull video amplifier configuration.

Any suggestions on the next step. Should I just find exact
replacement parts for both Q351 and Q352? If so, do I need to find a
matched pair?

Thanks,
Andrew