On May 1, 12:42 pm, "Dave" wrote:
I have a mid-80's HK integrated amp (PM-650). It's been very reliable

snip

Any replies greatly appreciated.

In no particular order:

a) cleaning pots and switches is only the first step. You need to
provide some (slight) amount of lubrication afterwards. 100% volatile
cleaners can cause serious friction after the skunge is removed
rebuilding additional skunge almost instantly. The idea is to exercise
the pot only as long as the cleaner is wet, then stop, then re-
saturate to rinse out the residue. *AFTER* that, a wee spritz of
lubricating cleaner makes all go smoothly.

b) switches are even 'more so' as wear can happen in any of several
ways including breaking of tabs or contact springs, and additional
friction can cause failure. So, same process. Saturate, exercise for a
few cycles whilst saturated, rinse, lubricate.

c) Look for broken traces on the boards, look (still) for bad caps. Do
you test the new caps *before* you install them? I have found about
0.5% of new electrolytic caps are bad or sufficiently out of spec to
be problematic. "Badness" typically manifests as intermittents... and
your delay may be related. Or, one you did not replace for whatever
reason...

d) you may believe that the power-amp section is clean, but one thing
I have experienced that is quite peculiar but as I have seen it
twice, it cannot be all that rare... an input transistor on the power-
amp side has become sufficiently different from its other-channel mate
that similar-volume signals to it are quite different in output
volume. RARE, and the only way you will catch this is to remove the
questionable transistors and put them either on a scope or tester that
can determine their actual response.

e) lastly and I have seen this only once and it was A BEAR to find. A
perfectly fine looking 1/2 watt resistor in the signal path had
drifted to 3X its nominal value. How did I find it? Well, every other #
$%^&*( part checked out, so I started measuring resitance "cold"
across both channels and comparing the results component by component.
When I found a difference, I started lifting legs about that point.
And there it was.

Good luck with it.

Peter Wieck
Wyncote, PA