Acoustic 470 PA Board Issue

[gbono]

I'm starting to believe this is the amp from hell. I spent way too much time trouble shooting and replacing the A/B channel lamps. During that process, a bit of lead triming accidentally shorted the 90V rail to the zener in the BJT regulator on the PA board. I had to replace the zener in the regulator and all those voltages are now passing to the other PCBs just fine.

Here is a link to another forum where you can find the PA schematic - http://music-electronics-forum.com/showthread.php?t=10360

The current problem is no output on the PA board - signal from the other two PCBs are loud and clear but right after the 47K reaistor on the PA input I get 12Vdc on top of the input signal. By the time the signal reaches the base of Q401 (differential pair) it's almost non-existent and noisey. Checked all the active devices in the circuit and they are passing.

The sad thing is that this board was working fine before the regulator ckt was damaged. Maybe someone else can see something I've missed.

BTW I've modeled this board in TINA and I get agreement on all the posted factory diagnostic nodal voltages.