I'm stumped and a bit frustrated. Working on a -32 Bally sound board. Installed new electrolytic caps and new header pins. Every chip on this board is socketed, so that was a bit concerning since someone did all that prior to me. Tone section seems to be fine...meaning it is generating the tones through what I call the digital section. It is the analog section that is causing me grief.

+5V, 43V are fine. The +12 Volts is fine if you do not have a speaker connected. If you turn the volume pot all the way down (quiet) and connect the speaker, the 12V is fine. As you turn the volume pot up and just begin to hear tones from self-test, the 12V is ok. As you turn the volume up, the tones disappear and you begin to hear a squeal come out of the speaker. The 12V drops to 6V as you increase the volume pot. This would lead you to believe the LM380N is bad. I replaced the LM380N with two different chips out of spare boards that work and I get the same result. I think it is oscillating, but I haven't scoped it yet.

If you just have the volume pot up a little when you begin to hear tones, the sustain works as it should. I truly believe the issue is between the U9 / U10 section.

Just for trouble shooting sake, I swapped Q1 and I always install a 1W Zener for CR4. No change. Nothing is getting hot when the voltage drops.

Even when the machine is in attract mode, turning the volume pot up causes the squealing and the voltage drops. You do not get the normal static sound of the pot wiper and background hum.

new electrolytic caps
removed the volume pot and put a jumper - no change
swapped U9 - no change
swapped U10 multiple times - no change
swapped all C9, C10 and other small caps - no change
new CR4 (13V Zener)
swapped Q1 - no change

All traces look good. I ohmed all of U10 pins to ground and compared them to my good board. Nothing was out of the normal.

Anyone have any thoughts?

OK, finally coming back to this after a busy summer and having another Bally SS game in the shop for rebuild.

And the issue was...R36 on the sound board. My 12Volts was around 11.6 and then 8.1 when sound was activated. The LM380 was going into oscillation due to the supply voltage dropping. It took me about 3 hours to find this because I pulled the 741 preamp and found the LM380 was the main issue. I tried different 380s and a few other things. It was not until I left the sound oscillating for a while as I scoped the supply that I noticed the supply dropped to 6V. I had already replaced the Zener and electrolytic caps as maintenance. But now I saw the real problem since the voltage was that low. I pulled R36 and it was 16K Ohms after getting warm.

This board came to me with every chip socketed. That is never a good sign! It is now my test board and happy to have it running.