Brenda Ann wrote:

"William Sommerwerck" wrote in message
. ..
This isn't criticism (no way), just a question...

Do you think this was a rational repair, or was it a matter of luck?

I'd like to hear a bit about how you finally decided (or discovered) that
this cap was the problem.


Very much a rational repair. I pride myself on my troubleshooting skills.


Good for you Brenda. that ids the only way to learn what is really
causing problems, and over time it lets you develop a skill set that
will let you fix almost anything.


Upon observing what happened as I kicked the filters/tone controls in and
out, it was easy to surmise that it had to be either the tone control
circuit or the first stage of the power amp, and that it had to be a cap.

Digging into the schematic I found that there was only one active component
per channel in the tone control circuit, and that only one cap could cause
the same problem with either of the two switches in the positions that
caused the problem.


Those Japanese tantalums were irritating. I had 8,000 identical
Jerrold cable TV boxes that used a 3.3 µF 35 volt Japanese tantalum
across the tuning voltage to the RF module that had at least a dozen
failure modes. The worst was an intermittent leakage that cause drift,
but only when it felt like it. I think part of the problem was the way
they were installed, with some strain on the leads where it was wrapped
around a feedthru and a ground pin, with very short leads.


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