I figured it out. there are definitely two rom revisions; I have two board sets here that both autolaunch the ball, and U6 is labeled "e-891-15 "... however, one of them was originally labeled "e-891-14" and the 14 has been changed to a 15. Must have been a factory update at some point....
I'm working on yet another Baby Pac-Man, and the right switch is removed from the right coil that launches the ball. The ball automatically launches on this one, and it was already like that when I got it... I think there are two rom revisions like we've been supposing, and the Alltek board...
100 Ohm pot, something like this would work, if you have any other Jamma Cabinets you can test your board in it to confirm but I've had about 10 of these and the sound pots are always bad in the cabinet...