Repair Log: Strangest Pac-man problem I've ever seen

LyonsArcade

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Repair Log: Strangest Pac-man problem I've ever seen

So, I've got a Ms. Pac man that I've been having issues with. The board works fine as a pacman, but when you add the daughtercard and ribbon cable, it won't boot (keeps resetting).

So, I tried 5 different ribbon cables (used!) and 3 made it do really crazy things, but two made it just keep resetting. Then I checked all the daughterboard roms, all seemed fine. I swapped out all 4 of the smaller proms, no difference.

So, I ordered more ribbon cables. I put a BRAND NEW ribbon cable on it, won't boot. Put the z80 back in, works fine as a Pac Man.

Started thinking maybe the daughterboard draws more power and maybe I've got power issues (I had already cleaned the edge connector, etc.)...

So I checked the fuses. I found one of the 7V fuses looked perfectly fine, but was at least partially blown (tested open with the meter).

The damn game would WORK without the fuse if it was a Pac-Man, but wouldn't work if it was a Ms. Pac Man because of the extra circuitry. Popped a new fuse in, works perfect.

In other words, NEVER ASSUME the power works just because the board is running. LOL.
 
Try upgrading all of the onboard caps; Bob Roberts sells a kit. The onboard power conversion may not have enough juice left in it to power everything. FYI: All of my games prior to JAMMA get new caps everwhere!
 
Yep, some boards will run fine with only one fuse and others wont.

I have one with a strange problem on the bench now, well its a new one to me. The board is dead but if I pull off the vram card it will boot and play(no sync obviously). Plug the vram back in and it goes dead again.
 
Must be a short somewhere, eh? Does it work with any other vram card?

Nope, tried a couple vrams and also a custom. I use customs when working on boards so I can get to everything. Once the board is fixed I throw a card on and retest. But yeah, something is shorted somewhere in the sync circuit I would guess.
 
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