Hi,

Sorry I didn't get back to you sooner, real busy.

The measurements you provided tell a lot about the health of the amplifier.

First, the Main PWM Power Supply is operating and providing +/- 36 Volts to the MOSFET Amplifier Output devices. This is the TL494 PWM, all of the circuitry on the Right side of the picture composed of the Power MOSFETs, dual diode bridge rectifiers, Transformer, etc. We don't know if there is any ripple without oscilloscope waveforms (to verify health of the large bulk storage capacitors that other list responders are concerned about are okay). I was concerned with the DC Voltage measurements on Q210, Q223, Q218 & Q211 though, can you re-measure them.

Second we see that the low voltage regulators are operating as the TL072 Dual Op-Amps have +/- 12 Volts on them. The pinout is different from the 4558 that I mentioned before, but, you have the correct voltages on pins 4 and 8. Again, we don't know if there is any ripple without oscilloscope waveforms.

I didn't see if you had checked for open ground traces or solder connections on the RCA Connector ground pins as Mark had mentioned. Did you do this and see anything there? With the other items being good, this is still a good suspected problem. I also didn't see that you had cleaned the controls, but noticed that these are likely sealed versions anyway. Have you rotated all of them through their range a few or more times to remove dirt and oxide build-up? The slide switches are also suspect, move them through their positions a few or more times too. Those could be cleaned too.

Once you have access to the back side of the amplifier board (Solder Side), check for open traces and poor solder connections as I mentioned and see if there are any of them in the Input and low-level amplifier stages.

At this point, it is time to provide an input and troubleshoot with an oscilloscope to locate the bad Op-Amp or missing signal. If you still want to fix it, we can go through that and find the problem. I would think that we might want to take that off-line though, then others won't have to read the long emails and may not be interested in how to fix this kind of problem.

Good luck,

Ross