The cap is not placed across the line, so it need not be a safety-rated one. If it shorts, the device simply does not shut off--no fire hazard there. Having a safety related one certainly would do no harm, though. The cap in that position suppresses arcing across the switch contacts, especially when the switch opens.
The left channel behaves perfectly so it really seems to me that there's something off in the right channel. Since I'm a rank amateur at this, i've been doing a lot of reading about how amplifiers work to try to narrow down where the problem could be. This circuit is pretty complicated though, for me at least. I think I need to focus on feedback resistors and capacitors. I'm just not sure I'll ever find a bad one with an ohmmeter or LCR meter since it only seems to act up when I turn up the volume.
Thanks for that. I'm thinking mine is something along the same lines. Since my left channel works well, my working theory is I've either damaged a capacitor in a feedback loop or I've got a bad resistor still in the right channel doing something similar to what was happening on yours. Mine looks more like a glitch in the sine wave rather than a uniform distortion. I don't know if that should make me lean toward bad resistor or not. I have found some out of tolerance resistors in it already though so I think I'm just going to replace them all and see.
I replaced the mica cap with a film one already so if I didn't melt it putting it in, I may have to try something a little bigger. I'll pop C816 out and test it. i don't think I have an extra film cap. Should have ordered extras. But I think the original silver micas seemed ok on the tester so I might be able to put one of them in just to see if it changes anything.
I just looked at the schematic for the AU-555 and can't see the crowbar circuitry, maybe you are thinking of the AU-666 which does have crowbar protection?
I stand corrected, and my apologies to you Ben, although I have just re-checked and those components are nowhere to be seen on the schematic I have.
A Sansui schematic is a "guideline, rather than a rule" (to steal from a certain pirate movie)....those components are nowhere to be seen on the schematic I have.
Yep, I found them on a block diagram.
I can certainly try it. If I understand the schematic right, it looks like I can just remove the protection circuit components completely. No need to make any connections where the protection circuit was. Is that right?
I tried pulling the protection circuit diodes and got no change in the oscillation. Also tried putting the original C816 mica cap back and got no change. Just because I had one, I temporarily tacked a 1000 pF cap to the underside in parallel with C816 and there was a slight reduction in the severity of the oscillation but it was still there. I took that temporary cap back out since it didn't seem like that path was going anywhere.
