Accuphase C-200 Distortion After Warm-up

[jbwrightsman]

Greetings!
I've had this Accuphase C-200 Preamp for several years now. Since getting it, it has exhibited some distortion in both channels after it warms up for a few minutes and only with low volume levels. If I give the signal more gain (volume) the distortion seems to disappear. The signal distortion sounds like a bit of static, crackling or garbling. The signal occurs at the output of the C-200 but not through the P-300 it is connected to. It occurs regardless of whether the tone controls are engaged and appears for all signal inputs including the phono stage. I was considering replacing the transistors on the filter/output boards but decided to consult the good folks on AK first.
I have a signal generator and an O-scope and can read a schematic but could use some help on where (which boards) to start signal tracing and what to look for. My diagnostic experience is limited.

Any help is greatly appreciated.

 

[reddish75]

Both channels the same after a bit of warm up?

Sounds like the powersupply, or ground common to both channels, look for dry joints if not try hitting those transistors with freeze spray when it's making that sound

 

[jbwrightsman]

After trying freeze spray I was unable to affect a change in the pattern.
I happened to have another good amp available so swapped out the P-300 power amp for the known good amp.
Lo and behold the problem disappeared. My conclusion is that it's not the C-200 in the first place, but P-300 with the problem.
On the P300, I've replaced all of the semiconductors according to recommendations found in other audio karma forums.
I've also tried swapping out the power transistors with new ones recommended by those same audio karma forums.
This has made no difference. Am going to open a new discussion thread to seek help with the P-300.