I'd spent several hours getting a Square Head up and running. (Finally found a jammed latch plate on the OB "O" sequence relay) Worked great for 15-20 games...then: when the ball is drained the ball count stepper (works smoothly manually) does not decrement a ball and the 20 unit bank doesn't reset, but activating the ball drain switch trips the delay relay and nothing resets; all the previously scored Xs and Os remain lit. When I manually retrieve the ball the game works fine, but still on ball 5. Everything resets as it should when I start a new game. Puzzling since I had played a number of games without adjusting anything and the problem arose.

I'm kind of new to this, so keep the answers simple, please! Ordered the schematic today.

All the Jones plugs have been cleaned twice.

Thanks for the responses. Moderately tightened all the all switch stacks and cleaned and checked change of state on relays on the main base board plus small bank on base. No change. Was hesitant to work on the score motor. No change. Then while playing one ball games (about 5-10 of them) and restarting the game after the initial drain, I heard the main bank activate and all is fine, plays as it should. Wish I knew what was causing the problem - sure it will reappear. I would think some switch is just barely making contact. Any ideas of the likely area to look at?

Continues to work fine. I'll mark as solved,