Pac-Man glitching

ieure

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This is a Pac I picked upa while back, which I stuck a 96-in-1 in. I played it a while back, but forgot to turn it off… It chugged away for 3-4 days before I noticed, because it's in my detached garage. It seemed fine, but the next time I went to play it, the text/ghosts/Pac started to glitch out intermittently.

I haven't started to diagnose things yet, just curious if people had seen this before. Presumably the ROMs aren't the issue… I'm thinking either power supply, bad socket, or a crystal. But I don't really know what the hell I'm talking about, and I haven't done any work on this or similar machines yet.

I looked through some lists of common Pac problems and didn't see mine. Also read through the manual to see if the test points on the PCB were labeled, but I didn't see anything there, either. I guess just find the +5 line on the edge connector and start there?

 
Very carefully, reseat the VRAM addresser module. Just be careful to not bend any pins.
 
Bad crystal? That will tend to prevent the whole machine from running at all.
Power supply issues? The glitch on the screen would not be so localized.
Bad socket? Possibility the data on the rom is not getting where it needs to be.
bad ram or VRAM adresser? Possible.

Simple things you can try.

Clean and reseat the EPROM and CPU on your main board.
Check the voltages to be sure your getting 5 volts to the board.

Good luck and post your results..
 
Bad crystal? That will tend to prevent the whole machine from running at all.
Power supply issues? The glitch on the screen would not be so localized.
Bad socket? Possibility the data on the rom is not getting where it needs to be.
bad ram or VRAM adresser? Possible.

Simple things you can try.

Clean and reseat the EPROM and CPU on your main board.
Check the voltages to be sure your getting 5 volts to the board.

Good luck and post your results..

I tried reseating the CPU. It's on a daughter board because of the 96-in-1. Made no difference. Whenever my cranky kids take their nap, I'll look at +5 and VRAM addresser.
 
I tried reseating the CPU. It's on a daughter board because of the 96-in-1. Made no difference. Whenever my cranky kids take their nap, I'll look at +5 and VRAM addresser.
Sorry I should have said reseat the Old z80 scocket.

The one Circled in Red..

The other ones circled in Orange should be reseated also.
 

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Z80 will have nothing to do with what he's seeing on the screen.
 
Z80 will have nothing to do with what he's seeing on the screen.

If resetting the VRAM adresser fixing the problem, it is an indication that oxidation has built up on the sockets in general. Reseating the sockets in general is a good idea unless the ic chip legs are experiencing corrosion issues.

I stand by reseating all the chips answer.
 
I honestly doubt that reseating the VRAM addresser will fix the issue, but it's the only thing that would be worth checking in that manner IMO. I think it'll have to be put on a bench and looked at with a logic probe and/or scope.

RJ
 
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