Another issue with my JITB. The machine has an intermittent startup issue where the score motor keeps spinning after it resets the score reels. Seems like it should be triggering the U relay to reset the control bank. The problem seems to have gone from intermittent to constant.

I did some troubleshooting. When I would manually close the U relay with my hand, the control bank would reset and the motor would stop. Then, I was trying to electrically trigger the U relay, using an alligator wire leading from the 25v supply. It wouldn’t work! And...neither would the relays adjacent to it. The entire rightmost bank of relays on the bottom panel is non- responsive.

After some more troubleshooting, I’ve concluded that the ground to those relays in the right-hand bank is broken. They’re floating ungrounded. Other relays, such as the knocker and chimes, are grounded. And the other bank of relays is grounded. And the score motor is grounded.

Ok-reasonable enough- there’s a broken ground wire somewhere. I’ve spent a few hours looking but haven’t found it, so I’m hoping to get some clues. Does anyone know what the grounding path is, generally speaking? Based on my observation, each relay is just daisy-chained to the next one. It would be awesome if I knew the order of the chain, so I could narrow things down. But the braids are so tight and bulky that I can’t even tell what wire is the source of grounds for that whole right-hand relay bank. I assume the schematic is not a representation of the actual grounding path- it just shows all the relays tied together at ground.

Maybe a jones plug is in the grounding path? But that doesn’t seem right- the machine can reset without the playfield present, which suggests the bottom panel grounding path doesn’t rely on the jones plugs.

Is there some ground-interrupt switch that isn’t in the schematic?? Surely not.

I guess as a last resort I could start adding parallel grounding wires, forcing stuff to be grounded. But I think I need to do a few more hours of penance first. Hoping people have some slick suggestions for narrowing down this issue.

Sorry I wasn’t so clear about the grounding. I measured an open circuit (megaohms) between the knocker ground and the ground for the u relay. Then I jumpered a wire between them and U fired properly under score motor control.

Well I was able to fix this. A black wire between two relays was separated from its lug. I needed to measure the resistance between each pair of adjacent relays, and that helped me find the broken link. Soldered that wire back in place and everything worked again.