Original VR1 is a UA78H05SC. The manual calls for a LM323K, Are these interchangeable? Can U use a LM323?
So after doing a full resto on a EBD, re-pinning all connectors and using a Weebly MPU, new Alltek SD and Lamp drivers, new rec. board, The S&T was not running. It would boot but not produce sound or speech. A few seconds after the game is turned on, a loud background hum starts, as the game warms up.
I remembered a while back that I had a Xenon that would not produce sound. After some digging, I found that the Alltek driver un-regulated 13.5V output was high, like 16+V. Going back to an original solenoid driver fixed the issue. Luckily it didn't harm the sound board.
So I thought this may be the same problem, and sure enough, it was. This time it's a brand new alltek Sol driver. It's putting out over 16V and the S&T doesn't like that. So I know the S&T works but I still have this annoying hum. U ungrounded the speaker and removed the mounting screws from the S&T. No change. I'm wondering now if the high voltage damaged the S&T?

Suggestions please!

I re-capped the S&T, installed new volume pots and replaced the regulator. Background hum is gone and the board seems to be working well.
I'm not sure which component was causing the hum but I'm glad it's gone.