After working on the MPU, the rectifier board and the regulator board I installed the rectifier board and checked the voltages - all good. Then I installed the regulator / solenoid board and checked the voltages - all good. Then I installed the MPU and the fuse for the 12 volt blew. I removed the MPU and re-checked it on the bench - 6 flashes - good.

Today I replaced the 12 volt fuse and rechecked all the voltages - every thing checks good. Then I reinstalled the MPU but this time I only plugged in J4. Turned it on and I get seven flashes.

This looks like (to me) that I have a short somewhere outside the MPU that is causing the 12 volts fuse to blow. I only have one 4 amp fuse left - any ideas where too look?

Thanks

Bob

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Thanks Ken,

I'm not real sure but I think it was shorted before - I found a blown F3 fuse when I was testing the rectifier board.

I repaired some corrosion and a burned hole under J4. (see this post : https://pinside.com/pinball/forum/topic/large-hole-in-mpu-100

But I'm confident the MPU repairs are OK. It checks out on the bench and I get seven flashes when it's installed with nothing else connected.

I did change the J4 connector because the original was burnt. And I replaced all the crimp on connectors. But I'm very careful when doing this - I mark each empty connector slot and only change one connector at a time.

I'm thinking the problem is in the sound board - it uses 12 volts - J2 pin 5 & 6 shows 11.9 volts. But J2 is connected and the 12 volt fuse is not blown.

Bob

Is it possible for a short in the 5 volt somewhere to take out the 12 fuse?

Thanks Ken,

I've considered those breakers before but they seem to be a waste unless you work on machines a lot. I have plenty of 5 amp fuses but only one 4 amp left. My next GPE order will include more fuses or some breakers.

Tonight I connected everything except the sound card and it worked. I even ran the self test and played a few games (no sound). I removed the sound card and looked it over but don't see anything obvious shorted.

Any idea what would cause a short on the sound card?

Thanks

Bob

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Today I installed a known working sound card from another machine. The good news is the fuse didn't blow but the bad news is I have no sound. I checked the voltage at TP1 and have 5 volts - at TP7 I have 13 volts.

Is there any way to check if the sound card is producing sound?

Tonight or tomorrow I'll try the questionable sound card into the other machine and see if it blows the fuse.

Thanks

Bob