Quoted from Robotoes:
Have you rebuilt/cleaned the ball count and player unit? That's where I would start.
I did and that solved quite a bit, but additional poking with it didn’t change the end of ball behavior.
So I just walked back in from my shop having checked a few things, and a few things have developed. In short, it looks like it was still on 5 Ball. I didn’t realize there are two places to set the number of balls: one in the back box, and one in the lower cabinet by the play meter. And as it turns out there were no bulbs in the 4th and 5th ball indicator sockets, so I didn’t realize it was still counting up. That aside I’m fairly certain the game still wasn’t ending until I cleaned and set the 3/5 ball contacts.
I also removed all the bonus settings as I think the extra ball was getting awarded a lot, and maybe contributing to the never-ending game.
So now I appear to have a 3 ball game that ends as it should (and hopefully stays that way!). The only thing that just developed is that the 3rd ball indicator light won’t illuminate (yes, it’s a known-good bulb). Does this come from the ball count unit?