Re: stereo amp cleaning


"Mark D. Zacharias" <spammenot@xxxxxxxxxxxx> wrote in message
news:cBd5i.2697$u56.42@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I think it's worth just replacing the bad resistor. Sometimes that's
all there is. Do check the various drivers and outputs for any
shorted or open junctions first, though.

R465, R485 Q415, Q417, Q419, R459, R457 all should be checked, as
well as the output transistors and the .22 ohm emitter resistors
R471 and R473. Don't forget the small value resistors like R469 and
R461.

I checked ALL of the resisitors in circuit and when I found one that didn't
jive with the expected value, I tested the same component in the other
channel. The resisitors used must be all 1% or better, they are BANG ON
their reported values... everything under 100 ohms was within 0.3 ohms and
this is a 20-plus-year-old amp.

R419, R421, R439, R445 and, strangely, R453 and R461 all tested open whereas
their duplicate in the other channel tested OK. R462 in the opposite
channel also tests open... It looks like about half the transistors should
be testable in-circuit, if one tests bad I'll pull and test
it(oscilloscope/curve tracer would save some time here).

Might take awhile.

Dave


.

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