Hi Everyone, I've been wrestling with a SA-7100 that has a horrid buzzing noise, for a couple of years now. I replaced electrolytics(including filter caps) and transistors using guides on this forum to no avail. Last night I used an android app to measure sound frequency, and found that when the pre and main amps are connected there are 60 hz and 120hz peaks, with many higher harmonics. With the pre/main jumpers disconnected, the 60hz is gone and I just have 120Hz plus harmonics. I'm pretty sure I have at least 2 different sets of problems. In any event, I borrowed an oscilloscope and started looking at the output voltages from the power supply board, thinking the 120hz noise would logically point there. Outputs at pins 6,7,12 and 13 were at the appropriate DC voltage and showed barely any ripple current. However, pin 11, which feeds the protection board, has a conspicuously larger ripple voltage(DC was okay). Looking at the circuit diagram(and trying to apply my rusty circuit theory) it seems that the pin 11 path,in contrast to paths for pins 12 and 13, doesn't have any smoothing capacitors in it, in which case the ripple current wouldn't be unexpected.Is this correct? I wanted to check with more experienced and knowledgeable folks before discarding the finding. Out of curiosity, could excess ripple into the sa-7100 protection board cause buzzing in the audio path? Any other things I should check while I still have the oscilloscope?