Hi all! I need a little help troubleshooting a WPC Indiana Jones.

Symptoms are a coil firing repeatedly in the multiball subway. Intended behaviour is that when the middle subway opto is blocked by a ball, it triggers a coil, opening the subway gate. The problem is, the coil continues to fire every 20-ish seconds afterwards, as if the opto is still blocked even though it's now clear. This continues throughout the game and in the subsequent attract mode. If you enter the operator menu it stops, and doesn't start again until the next time the opto is blocked in game/attract.

The opto is working completely normally in switch test, nothing unusual. The coil is also working fine in test. I've cleaned then replaced the opto transmitter and receiver with a known working pair, no difference. I've also tried swapping over the whole power driver board just to rule it out, no changes.

Now I'm a bit clueless on where to look next. My next guess would be something on the CPU board, but I don't have a compatible donor board to test that, and I didn't want to start poking it until I knew where to look. Anyone have any ideas, or seen something similar?

Thanks for your thoughts!

Thanks FatPanda! This gave me a direction to go in.

Unplugging the opto group connector from the 10 opto board does result in the subway soleniod stopping (but leads to another firing instead, unsure if that's intended behaviour when the whole connector is pulled). This led to finding some questionable prior rework on the under playfield opto boards, so I'm going to clean that up for now, repin the old IDC connectors to crimped ones, and socket + replace the LM339's for good measure. Will report back on how it goes.

I'd wondered this too actually, I don't recall seeing a flicker but I'll double check that. I'd previously ruled it out because the behaviour was identical regardless of whether I'd left the opto blocked or just triggered then cleared it. The coil also fired with consistent timing - if the opto was being intermittent I assumed the timing would've be more random, or would have done the initial trigger spontaneously by itself without needing me to manually block it first.

Reviving this thread to post the solution.

A quick recap: the machine is switched on during the workday. Occasionally when I'd check on it, the subway coil would be firing and would not stop unless you reset the machine or entered the operator menu. This problem was intermittent, making it hard to trace. Also, rarely, the idol would eject all balls during play.

The answer turned out to be questionable prior rework on a bridge rectifier. A previous owner replaced BR5 on the power driver board with an equivalent that had the wrong legs. To make it fit, they soldered leads to the legs then soldered those leads to the board. This worked fine until the solder cracked on one leg, causing a flaky connection that would occasionally wig out and fire a whole bunch of optos - notably causing the idol to dump all its balls, the machine to lose track of ball placement, and think there was a ball in the subway. If that subway opto is triggered, the machine will continue to fire the subway gate coil until a ball passes up to the idol - as there is no ball to pass, it just keeps on firing.

Here's a brief video I took at the time showing the rectifier.

Hope this is of help to anyone else tracing odd issues!

That's a good point! The answer is that I'd misunderstood how the subway logic worked. I'd thought the coil gate was supposed to fire only while it's opto was blocked. In actuality, it fires on first block and continues to fire until the ball rolls through and activates the next switches in the subway/idol chain. If there's no ball to roll through, it keeps on firing and doesn't stop.

Now, the only symptom I'd seen at this point was hearing the coil occasionally doing this when I'd check on the machine. I'd figured out that you could trigger it by activating that gate opto, but I hadn't realised *it was intended behaviour*. So when trying to eliminate things I swapped the driver board, activated the opto, found the coil still kept firing, and incorrectly thought that meant I still had a problem.

So, for any folks trying to diagnose the same problem, your issue is with the subway gate opto switch triggering. If that's your only symptom, then check the gate opto wiring path - look for cracked solder joints or frayed wires on the opto send/receive, make sure the wire housing is still terminated correctly, and that the header pins are clean and don't have any cracked solder joints. If you have multiple symptoms, the problem likely lies elsewhere. In my case, when I finally saw it happen in front of me, the idol ejected all balls and the game lost track of ball count. Voltage to all optos had dropped, causing all of them to trigger as blocked at once. This led me to checking wiring on the driver board - wiggling connectors near BR5 triggered the symptoms, and a light push on BR5 confirmed it as the culprit.