"ixuv" wrote in message
oups.com...
Hi

First at all I have to say that my English is little bit rusty, but
hopefully you understand what I try to say.

I have this Sony 7.1 channel receiver which makes a crackle(is it
right term?) noise in front left speaker (A+B) and headphones(left ch.
also). The noise appears when I adjust master volume, input selector
or mute. There isn't any differences if I adjust these from remote or
front panel. When I adjust master volume, noise appears only between
these dB levels, which is strange:

-53,5 -54,0
-61,5 -62,0
-69,5 -70,0
-77,5 -78,0
-85,5 -86,0
-93,5 -94,0

Without this noise, receiver works properly.

I have service manual for this and I already checked these:

-muting transistors - ok
-op-amps and capacitors near audio selector and electrical volume -
ok

What next?

That's an odd one. What might be a clue is that the next point that crackles
is always 7.5dB up on the previous point, which would suggest that it is
something 'digital', such as the volume control IC. I seem to have the
service manual for just about every other STR series amp from around that
time, but not the DB795, so unfortunately, I can't look any closer. However,
I would say that often, the volume control IC also does input selecting, so
it would be worth having a look to see if that is the case with this amp. I
have had these ICs go faulty, and this is the sorts of problems that they
can cause. I had one recently that kicked up a lot of noise on one channel,
above a certain volume level. I would think that you would be able to see
this crackle on a 'scope, and then know for sure where it was getting into
the chain, but failing that, dabbing a 0.47uF cap to ground from various key
points, such as the output of the volume control IC, might prove revealing.

Arfa