I recently fixed up a Grand Prix for a friend, and it just recently developed a new issue with the hundreds reels on the 4th player running non-stop during reset.

To fix it, i adjusted the switches on the reel but that still didn't seem to solve it. Remembering a problem i had with the game early on, i checked the player unit and noticed the disk was out of alignment. Positioning it correctly finally got the reels to all reset properly. So, i took the player unit disk off and adjusted the board to properly position the contacts on the disk.

Once i got it back together, everything was working ok except i happened to notice the 1k reels weren't advancing the 10k reels when they switched from 9 to 0. All 4 players are exhibiting the same issue. The 10k reels will score when activated individually (for instance double bonus counts the 10k's properly) and all the other reels advance the following one when they turn from 9 to 0. Strange problem, especially since it's affecting all 4 players.

Any suggestions? I'm betting i messed something up when adjusting the player unit, i just couldn't find anything loose or broken...

Thanks!!!

Thanks for the advice, guys! I like the jumper idea, hadn’t considered trying that. I’ll hopefully be able to stop back over there in the next day or two to take another crack at it.

On second thought—is it possible to put the disk on the player unit the wrong way? It’s keyed so it could only go on 1 of 2 ways. Is it possible I just need to take it off, spin it 180 degrees then put back on? I was assuming the contacts on the disk are the same arrangement all the way around but I didn’t get a closer look before I left…

Also, thanks HowardR for posting the relevant schematic portions—I finally realized I was only seeing part of the scoring reels schematics and hadn’t ventured far enough down to find more listings for the scoring reel coils, including the circuit i was trying to find in vain in the upper area. Those schematics are ridiculously long!

I’m certain I’ll finally catch the culprit soon, just needed a nudge in the right direction. Thanks again, guys! I’ll report back with the solution (or more questions, lol)

I’m also starting to suspect a wire connecting the 2 wipers on the player unit might have broken off one of the solder lugs, forcing that particular circuit open. The jumper wire is really gonna come in handy…thanks again for the suggestions!

My man!!! Thank you pinballdaveh you never cease to amaze me, lol! I'll report back after i get a chance to rotate the disk. That's gotta be it!

This is exactly what the problem was! I took a pic of the disk while i had it out, you can see the extra wipers on the bottom half. PXL_20240214_192137674.jpg

Turning the disk 180 degrees got everything scoring correctly on all 4 players.

Thanks again, Jukester for the advice (you were right--it was indeed the player unit), HowardR for the tips on using a jumper for troubleshooting and schematic referrals, and pinballdaveh for zeroing in on the culprit. You guys rock! Grand Prix is firing on all cylinders once again