I purchased a Pioneer SX-750 a few months ago in good condition. Both channels operate on all inputs, lights were all out, generally dusty and dirty but in good shape. I was informed by seller and verified in testing that both channels have a low level hum like a ground loop buzz. I decided to continue the restoration thinking I could isolate and fix the problem. I replaced all the lights with LED's, cleaned all pots , cleaned and polished everything, re-veneered the wood and now the receiver looks and sounds great except for the buzz. I went through all the subassemblies looking for the issue. I thought I had isolated to the Power Supply and Protection Assembly. I replaced 8 caps on that board, checked all grounds and even bypassed the protection circuit and relay altogether but the buzz remains. So ... here is the symptoms and the question is, has anyone run into this and solved it. Like many things mass produced, you find one unit with a problem and there are more than likely many more with the same issue. 1-Buzz appears in both channels at a low volume level that is only heard during quiet. 2-Buzz is present at all volume levels but does not increase or decrease with the volume control. 3-If the receiver is powered up with volume at 0, buzz is most often gone. Turn the volume up, play something and then turn back to 0 and buzz is present. Any help is appreciated!