Hi All. I'm very new to the pinball hobby and recently purchased a Gottlieb Pro Football off Craigslist. It's in generally really great condition and works well, I'm having a blast with it. I've even fixed a couple minor issues already (one with a score reel not advancing and one with the football yardage not advancing). The last problem I'm left struggling with is that at seemingly random times during a ball drain, the ball in play number will advance by 2 or even 3, instead of just 1. It doesn't seem to matter which ball I'm on or what I'm doing...sometimes the problem doesn't happen at all during a game and sometimes it skips 2 or 3 balls, frustrating! The game is set to 5 balls. I've extensively checked out the O (Ball return), P (Add ball count unit), and Q (Ball return control) relays but they all seem to be well adjusted and working okay, at least as far as I can tell. I've also checked the scoring motor, specifically 4C, 3rd and 4th switches, pertaining to ball counts. These seem to be working well too. The stepper in the back that controls the ball in play also seems to be working fine, it steps up one at a time correctly and resets all the way down with no issues.

I do have a schematic but I'm still very much learning (and struggling) to read it. Does anyone have any ideas on what I can check to remedy this issue?

It's hard to get high scores when you never know how many balls you're going to get!

Thanks!

Thanks for the reply!

When the outhole switch is closed, the Q relay activates and there is no chattering at all that I can see on that one.

Normally when I'm watching it. I see Q activate when the outhole is closed, then P activates, when P is done, O energizes and goes into a hold mode until a point is scored. When a point is scored, the O relay de-energizes and when the ball drains, the process starts again. When the problem occurs, (to my novice eyes) it looks like P activates and advances the ball count, O energizes momentarily (and must de-energize quickly), then P will activate again advancing the ball count again. It all happens very quickly. I've tried getting a video of it happening but every time I try, it seems to work fine...as soon as I start playing it will happen again. Ugh.

Thanks for the tip! I'll check it out in a few minutes

Hmm, no success yet. I checked out the motor 2B switch and it looks well adjusted. My flexstone is shot and I have 2 more on order so I'll clean it better when they arrive. I tried a bit of sandpaper, then alcohol in the meantime.

Thanks for the 'last ball' suggestion...unfortunately, that is not the case in this scenario. The ball skips occur at totally random times, sometimes even right at the start of a game...it will go to ball 1, then immediately switch to ball 2.

It's frustrating because the rest of the game plays amazingly well and it's so fun. I'm determined to figure it out though!

Great suggestions, thank you.

Here's what I tried: I started a game and allowed O to energize, then manually de-energized it and put a piece of paper between the lock-in switch. At that point, I could close the ball outhole switch and the ball in play advanced normally each time, no skipping... I tried this for about 6 games or so. This *seems* to be the problem!

I checked out the NC N, M, and L switches and they seem to be gapped well. I will work on cleaning them better once I receive my new flexstone in the mail. For now, the problem is still occurring so I'm hoping it's just a dirty switch in one of those relays.

I would just bypass having O energize for now except the game won't start without it energizing the first time.

Thanks so much for the help...I will keep working on it.

Got my flexstone and cleaned the switches. I also had to clean the switch in the back of the stepper unit...now all seems to be well with no ball skips!! Thanks so much for the assistance.