I noticed that Jumping Jack was inconsistently scoring the bonus. On observation I found that the discrepancy was variable and seemingly somewhat random. Rarely it would award all of the earned bonus but for the most part would award 40-80%.

I watched the “add bonus scoring unit” coil and noted that it would stay energized for 2-3 pulses 1-2 times per cycle. Thinking that it might be mechanical I took it apart and cleaned it and it did not change behavior despite moving easily by hand. Just to be sure, I “grounded” the coil rapidly with a jumper wire and it performed normally.

From the schematics, the coil should pulse only with score motor switch 1A while the E relay is energized or the runout switch is closed. Yet even after blocking all of the 1A switches, the coil would still energize erratically. The schematic shows a lot of connections with other relay circuits and I assume there is a switch or 2 or more somewhere that are closed when they shouldn’t be that is creating a “back-door” circuit completion for the “add bonus scoring unit” coil but I don’t know where to begin.

Your help is greatly appreciated.

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I checked the switches which looked ok and cleaned them for good measure but there was no obvious change in the behavior.

The M/B on O relay did look maladjusted. I cleaned and gapped the switches but still no noticeable change.

I’m 99.9% sure the problem is not in the unit itself. Something is firing that coil inappropriately. I am just at a loss on how to narrow it down.

Tested and functioning properly.

Any further insight before I descend into the rabbit hole is greatly appreciated.

Problem fixed!

Big thanks to HowardR for his generous help and teaching me the importance of observation.

We were troubleshooting the possibility of a short somewhere in the OR-BL wiring. Disconnecting the OR-BL from the back box connections had no impact. As I was following the wires in the bottom board I found a screw that had fallen into the score motor next to the 4B switch. How I failed to see this earlier I have no idea. Anyway, I removed the screw and the bonus scoring and coil behavior worked perfectly! As you can see from the photo, the issue was quite remote from the add bonus scoring unit circuit.
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