"Mark D. Zacharias" wrote in message
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Dave wrote:
"Mark D. Zacharias" wrote in message
...


Man.

This might be really easy. Q 405 conrols the turn-on delay. HK's don't use
relays, so they mute the signal til the amp stabilizes. On this model it
is Q405 and Q406 respectively. The transistor could be bad, but I would be
especially concerned with D401, R405, C405, C407, and D403, which is a 15
volt zener.

Could just be solder connections relating to the above, but in any case
you need to see that Q405 turns off hard a few seconds after turn-on.
The -12.5 or so volts at the base is critical.

Mark Z.

Mark:

First off, thanks very much for all of your insight and time.

Okay, as I had just "upgraded" C405 and C407, I put the originals back.
Left channel is now functional once again, although I haven't had time to
check my voltages yet nor have I given it a good listening test. I can't
say why, but I've got a gut feeling my voltages are still on the high side.
How common is it for zener voltages to wander over three decades?

I set about setting the idle currents and, as soon as I touched V404 (right
channel), poof, right channel gone. I think the 1K pot just disintegrated
when I moved it after 30 years of sitting in one position. Well, I must be
doing something right, because I stumbled across a 1K 70's style (BIG) pot
in one of my many doorstops which I am cannibalizing to make myself an ESR
meter. I'll put it in tonight, hopefully it's in better condition than the
one I'm taking out. One wonders at moments like this whether one is moving
forward or backward...

I can't believe there are so few companies that make ESR meters... the more
I get into electronics repair, the more critical such a piece of equipment
becomes. Ditto with a transistor tester although there seem to be tons of
those on the market.

I have a hard time with transistor theory... I understand what they do, but
get quite confused when I see a whole bunch of them tied together,
controlling each other with various feedback schemes. That's when I start
testing components as I lack the deductive skills required to narrow things
down, as you did, to a single transistor and associated passive components.
Hopefully I'll get better at it... I've read some texts but don't find the
ones I've read particularly helpful. They all seem to assume that one is in
a laboratory environemnt at school with access to and training on the SPICE
program, in particular. Which I do not have.

An oscilloscope and signal generator are handy, but again is somewhat hit or
miss (for me) when I get into a transistor network as it's not immediately
obvious where the signal path is. It's almost easier in a newer amp with
IC's... what you end up doing is replacing an IC with ten transistors in it
because you know the problems's gotta' be in there someplace if you've got
signal going in and none coming out. If the IC is not obsolete and/or
proprietary and hence unavailable. In the past I've used the scope to
localize distortion which saves A LOT of time and lifting of legs to test
components.

I am quickly learning that with vintage audio gear, if it ain't broke, don't
even breathe on it or else...

Thanks again for your help.

Dave