When I power the AU-317 on I get large voltage swings from the pre-amps. Both amps exhibit this behavior. Measuring with a voltmeter, the voltages swing from +/-2V and decrease to 0V. I have not looked with an oscilloscope, but it appears to be sinusoidal. After the voltages calm down, I install the pre to main jumpers and I can hear some crackling coming from both speakers. Playing music with the volume up a little ways drowns the crackling out. I checked the +/- 28V supplies. They appear to be rock solid. I have attached the left channel pre-amp/control amp schematic. The chart shows turned on after being off for 2 hours, then turned off, then turned on, and then turned off. Any places to start diagnosing the pre-amps?