Re: stereo amp cleaning


"Mark D. Zacharias" <spammenot@xxxxxxxxxxxx> wrote in message
news:FMf6i.7530$4Y.6327@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx

P.S.

At this point I'd say it's a virtual certainty that the outputs ARE bad on
that channel. Probably the only reason it's not just blowing fuses is that
one or both of the emitter resistors, R471/473 are bad also.


Checked the outputs... they test OK on my transistor tester! No leakage,
both PNP and NPN had gain, although not anywhere near the same amounts... I
assumed they'd be "about the same"... anyway, the outputs ARE NOT shorted
and R471 and R473 DO NOT read open circuit although I haven't pulled the
resistors yet to test.

Started pulling transistors from the beginning of the signal path, tested
Q401 through Q413 so far, 5 more to go and they all test okay, no shorted
junctions and all show gain.

If it's a heat-related issue with a failing transistor, I'll never find it.
I don't think it is, because the DC bias on the outputs shows up right away
when the amp is powered on.

I'm out of ideas if the transistors all check out okay. I'm inclined to
blow $8 and replace all but the outputs, replace the half-dozen smoked
resistors, put it all back together and see what happens.

Dave


.

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