I had a similar problem with my first EM. In my case, the game would get to ball 5 and just stay there indefinitely. I checked the Game Over and other relays with no luck. Then someone suggested I re-check the ball count stepper. I thought I had cleaned and lubed everything on it, but there were actually two "hidden" fingers on the stepper, down on the bottom of the wheel away from all the others. Sure enough, as soon as I cleaned the contacts on those, the game ended properly. They were effectively the game-over fingers on the count stepper.

That was a Gottlieb though, and Bally is a little different. I'm curious, if you play more than one player (let's say 4 player game), does the game keep rotating through the Players' turns, or does it get "stuck" on one player eventually and just keep playing that person over and over?