The internet seems to lack quality troubleshooting information for WPC-89 sound boards.
I'm not sure if it's a matter of the boards not failing often, the repair being above the skill level of the 'average' pin tech or what.
Regardless, I've got *3* to repair. I picked the nicest looking one first, because it made the most sense to start working on the one that is the best overall condition. Plus, of the other 2, one had a big scorch mark where at least 1 cap caught fire, and the other is missing a few parts.
The board is unhacked. It has had some solder reflowed on the back of the board, and may have had the amplifier replaced, based on a little flux residue around the amp. But, no ICs have been replaced, etc.
It produces no sound. No hum, no clipping noises, just no sound.
I buzzed out the amps legs to the schematic, to make sure I don't have an issue with previous rework - all 5 legs are connected to where they *should* be conected.
I tested the ROM, 6809 and both Yamama Sound ICs in my test fixture sound board, and they all operate fine in it.
The board gets +5 and +12 from the driver board, and both those voltages are present.
It appears the 4 fat diodes, 4700 uf caps, and voltage regulators produce +12 and -12. Both those voltages are present.
The processor is running.
So, can someone point me in the right direction to do some troubleshooting? I read on Pinwiki that dried out caps can cause some issues, but those all seemed to tie into problems with sound quality - not with getting no sound.
Any nudges, gentile or otherwise, or suggestions, are appreciated!