Working on a Bally Black Belt. Forgive me as I don't have much experience working on 6803s. Not mine, but I have seen this pin play recently. It was out on the floor for a while and it was reported to me that either the GI or feature lights went dark. The diagnosis was unclear. It is worth noting that though I don't capture it on the video, some feature lights and some GI do light up on boot sequence. It was wrapped up before I could review any issues and then I brought it home to fix. Anyway, I fire it on, get three flashes from the sound board, nine from the MPU, which is what I am expecting for a successful boot. However, all I get is a repeating trough solenoid firing and a flashing light at the plunger. See video for MPU boot and issue.

Any thoughts? I have reseated everything, put new batteries in (they are off the board and no acid damage), and checked all the fuses.

Here is the video of boot: https://imgur.com/a/b2dXAla

Thanks so much for your help!!!

Fun stuff! Thanks for the advice. wayout440 is your level of confidence that this will require some significant IC work high? That might be a little beyond my pay grade but I can do light board work, reflow cold solder joints, rebuild molex connectors etc. Does anyone have recommendations per where I may want to start in checking off those types of repairs before I send the board out so I'm not grasping at strands? I don't want to have to jump through that hoop before I am certain that this is the issue.

Update: I have resolved the issue. I don't have a homerun answer, but I just started from scratch. Pulled all molex connectors again, blew everything out, made sure all pins on the boards were extra clean, rebuilt a questionable molex. It was definitely a connection issue somewhere along the way... and as an added bonus, the full GI and feature lights are back. Took a few hours to get everything pristine but it worked. Thanks to wayout440 for taking a crack at helping.