Neal, I have the drawings, but they are very large fold out things, they are the size of a road map. Very hard to scan. Frankly I'd just order the service manual from Yamaha, they want probably $15, but it is a very thorough manual - schemos, layouts, parts lists, biasing procedures, disassembly, you name it. Yamaha makes great manuals.
SOunds like your problem is in the power amp. Open it up and see of there are any Molex connectors involved. Pull them apart and then remate them to freshen the contact surface. Also, get a can of freeze spray and chill sections of the board until you hit something that responds. That is what freeze spray is for.
You can leave the speaker load not connected, and watch the noise output on your scope. Even a meter set to AC volts would probably measure the noise level. After all, when we freeze things all we care about is does the noise disappear or not.