So my Bally Old Chicago was working fine. Now it has suddenly developed an issue. When the last ball drains it begins to count the bonus but never stops counting. Thus, the game never resets. It just sits there racking up bonus points until I manually trigger the bonus step down coil and manually count it all the way down to zero. Thing is, this only happens on the last ball. The bonus unit works perfectly fine the rest of the time. I cannot figure out what's happening. I've included a link to the schematic on ipdb. Anyone mind taking a look and offering some suggestions on what to check?

https://www.ipdb.org/files/1704/Bally_1976_Old_Chicago_Schematic_Diagram_continuous.pdf

Howard, It seems like no matter where I jumper from in the circuit you highlighted the bonus step down coil fires nonstop when the last ball drains. If I remove the jumper during this endless cycle the game ends like normal. I also cleaned the score motor switches in that circuit. Didn't help. It's so strange that the only time the coil doesn't fire is during what should be the game over sequence. It functions flawlessly during all of the other balls.

I GOT IT! For now.....lol. So I kept messing around with the jumpers. Kept systematically going through every position to jumper from over and over. I noticed that when I jumpered the gray/yellow wire to the brown/white wire on the ball count unit and kept poking around on it I finally got the game to end! Seems like the wiper arm was not making good enough contact to the appropriate pad to be able to pulse the bonus count step down coil. So even though I already cleaned and lubed the ball count unit, I went ahead and gave that particular arm and pad a light filing and bent the arm to put just a bit more down pressure on it. Voila! Old Chicago is back to kicking my a$$ with those damn lower pop bumpers! Thanks for helping me narrow down the circuit to investigate Howard. Much appreciated.