Punch 500a2 messed up channel
 

Power was applied backwards to this amp and it took out one channel. I found Q122 and Q123 shorted, those were replaced. I still can't track down the culprit. Here are a couple wave forms. One is from the collector of Q103 and the other is from output (2012-03-20-22-55-30_126).

If there is no DC on the output, connect a dummy load to the channel, drive a sine wave into it and post the waveform on the output.

No dc on the output.

Waveform is missing the lower half. The signal looks ok until Q102 and Q103, it gets squared off.

Does lifting D104 allow it to produce clean audio?

Nope, tried that already.

Are the 20 ohm resistors connected to the emitters of the drivers within tolerance?

If the 20 ohm resitors were bad you would think there would be DC on the channel?

Those were replaced when the transistors were replaced. I will double check them.

Back to fumbling on this amp. Q122, Q123, R174 and R175 replaced. Still no lower half of the sign wave with D104 lifted. D104 cathode -37.14Vdc and anode -36.74Vdc. I have -3.8Vdc on the cathode of D204 in the good channel.

Are those voltages for D104 on the solder pads or have you reinstalled D104?