12v Short on Jamma board

intrnlstorm

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Hello everyone - Long time reader, new member and first post here.

I acquired two cabinets this summer. I grew up in upstate NY and we had a camp that had a rec hall with 30-40 arcade cabinets and 20 or so pinball machines. It was a great place to hang out in the evening or on rainy days.

Fast forward 20+ years. I camped there is summer and after the manager and I got to talking about the old days he told me that they still had some of the old games "out back". They didn't want to sell the working ones, Golden Axe, Double Dragon, Q-Bert etc. but would sell me the non-working ones for cheap. I settled on a 4 player TMNT and Black Tiger. Two of my favorites, so I was pumped.

The turtles needed cleaning and a new plug but works great!

The Black Tiger wouldn't turn on and after a couple of hours diagnosing it, I figured it out. The 12v on the board was shorting out the powersupply. I disconnected the 12v and the machine booted up and I played for a while without sound.

I took the board out and confirmed that the 12v pin and ground pin had continuity but now I'm stuck with what to do next. I have a variable volt/amp power supply (HY1802D) and a Multimeter with enough knowledge about electricity to try anything.

1. Does the 12v pin on these old boards just control the sound?

2. What would cause a short on the 12v?

3. Does anyone have a suggestion on what to do to fix it?

I'm only into each cab for $100 so I wouldn't be heartbroken to buy a new PCB but I would love to try to fix the original board.

Thank you for what ever help you can offer.

Joel
 
+12 is usually for sound most CPUs and RAM/ROM just run on +5.

I'd cut the pins in the circuit near the sound amps until you find the short.
there are a few other ways to find shorts too that a decent.
from using a ESR meter, or just hooking up a computer power supply and attaching the ground and +12 rails to melt the shorted component. but I"d probably just clip the power on the few chips that use the +12 one at a time.

-brian
 
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