Subwoofer amplifier no signal out of input board

[Fried Chicken]

I have an Allison AL10 which is a fantastic subwoofer, mated to terrible electronics.  Unfortunately the terrible electronics are now rearing their terrible head and the thing isn't working right.

I already replaced every capacitor on the board, and then I started poking around with the oscilloscope.  The signal seems to die somewhere on the input board, the amplifier side seems to work.

I hate to do this, but I've made a thread on an audio forum describing what I've done/looked at so far.

I can't find the schematics anywhere.

I'm currently suspicious of the Zener diodes, but if they've failed, idk how to replace them w/o schematics or part #'s.  I can't test them if they've failed, and I can't decipher any numbers on them either.

Maybe the best option is to buy a different higher quality plate amplifier.

I tried to attach images in a neatly organized fashion but wasn't able to.   Images of the input board, amplifier board, vertical section of the amplifier board, and a # from the PCB attached

[Audiorepair]

Look at all the small black transistors (Q1, Q2 etc) to see if any are JFETs.
These are usually marked J*** and are often used as the muting transistor(s).

You might get lucky and find one, and it is faulty, so the pre-amp is permanently muted.
For some reason these mute Jfets seem to fail more often than most other components.

[Fried Chicken]

I'll give it a look.  There is a bypass option on the input for auto standby, which I would expect would bypass any muting circuitry

[Audiorepair]

Mute Fets have a habit of failing short, thus permanently shorting whatever signal they are meant to mute.
There is no way to bypass that.

You can just cut them off the board to get the thing working.

[Fried Chicken]

When I checked the signal I didn't see anything.  What sort of signal should I see?

I can of course just pull the fets and test them