Quoted from aobrien5:
Is there anyway to "manually reset" the board? The one that stopped working seems to be in that state, but a reboot obviously doesn't help.
Full disclosure, I got the "new" board working by doing something totally boneheaded. I pulled it out of the game and set it on the front of the backbox to test voltages. While putting it back, something touched the ground braid, and the game rebooted. After that the sound started working again, but not for the original board.
Break the sound board into three sections.
The CPU stuff
The sound input stuff
The sound amplification
For the CPU, diag it like any 6802 computer. You need a clock pulse (External clock cpu p37). High reset (p40, DO NOT FORCE RESET HIGH if low YOU WILL BLOW UP THE 4011 chip). If the eprom /CE is pulsing and the CPU is doing work let the game mpu boot up all the way (or use SBM or other old software). Push the diag button and monitor TP4. When sound is playing TP4 (i think it is VMA) will start pulsing. If that looks good continue
For sound input stuff put the game in sound test and monitor the sound signals coming in the sound, inverting through the 4049, and then to the sound chip. If they all make it to the sound chip keep going. The sound chip can fail and not decode sound patterns properly, so keep that in mind.
For amplification problems introduce noise with your finger on a probe. If you get low, but adjustable volume the preamp is usually the cause. Zero sound and the CPU is running and the sound inputs look good, try the main amp.
The Bally 560-3 repair manual is very good for this board and way more detailed than what i typed out. IF you can follow the Bally 560-3 book, you can fix your board.
around page 77 in that PDF file.