I had a hard time discerning what part went with what channel, so I picked both of them. Sorry if I confused you.
I have seen a lot of issues with electrolytic caps used in the coupling circuits of the audio path. These 1 uf to about 4.7 uf should not be electrolytics. Metalized polyester would be a better choice in the audio path.
The voltage readings I was after was for E/B and C for Q101/102
I'm having a hard time believing that this may be power supply noise, but I have not seen anything like that before. I didn;t look close enoghh as to whether o not the amp supported multirail supplies.
I'd have to print the schematics and look a bit closer.
If this AMP has a tape monitor loop and or main/ pre out, Is suggest reversing the L and R channels there, to isolate the amplifier at fault or just disconnecting. The tape monitor loop usually has the same effect.
In rebuilding, I'd primarily change the coupling caps to metalized polyester and I would put ZNR's across each of the amplifier filter caps if they are not there. I'd think I'd wait, until the issues is fixed, though.
The general rule for troubleshooting are essentially:
1) Inspect and/verify customer's complaint. You could find roaches or loose screws or even sandwiches in a VCR. Brand new auction site stuff needs an inspection before power up. Your past that stage.
2) Check ripple and power rails everywhere. They are a no-brainers. I didn't look close enough to see if the L and R channels used the same power rail. Consumer stuff usually doesn't An amp I built does.
3) Isolation
True, you have it down to the right channel, but you can cross the left and right channels at the tape monitor and/or pre/main inputs/outputs.
You have at your disposal, injection and bisecting the signal path and you can even remove the main.pre jumpers and see what happens at the output.
You have a schematic and you can use comparison.
I might even consider thermal comparisons between left and right. Finger, thermometer or an IR thermometer. If something is oscillating, it's probably heating up more.
I didn't catch the frequency or the magnitude of the noise at the speaker terminals. The DC voltage at the speaker would be useful too.