Ms Pacman Crash and Resets

[yourbestscott]

Hey all,

Picked up a Ms Pac-man cabaret from PA a few weeks back. I got it functioning more than when I picked it up, but I can't seem to get past this issue and was hoping someone could point me in a direction.

When I bought it, only a few sprites would show up on the screen.

Initially, I thought it was the VRAM addresser board as when I reseated it, I would get double of the Bally/Midway box on the screen, and after screwing with it more I could get a fairly consistent picture.
20% of the time it would crash before the introduction of the ghosts.
The other 80% it will crash when the first maze appears.

So I bought a new one, no dice. Same issues as before.

Seeing as there was a bit of corrosion in the socket itself, I replaced the socket. No dice on that either.

This is where I'm at with how it plays. The video will describe it better than I can.

The crash is mostly inconsistent. Sometimes I'll get a full maze, sometimes pieces missing, sometimes 80% of the maze is missing, sometimes it'll crash adding a single credit, sometimes it'll crash before it even finishes drawing the Bally/Midway box.

I don't know great places to check for voltages but:
Off the 10,000uF caps I get a solid 5V.
Off the 2200uF 25V cap near the volume knob, I get about 12.2V.

Any direction would be appreciated!

 

[Scott C]

Original Midway board? Using Aux PCB?

Scott C.

 

[yourbestscott]

Original Midway board? Using Aux PCB?

Scott C.

Yeah, it's the original Midway board. I'm assuming the Aux PCB is the one the ribbon cable attaches to and is mounted towards the coin bucket?

 

[Scott C]

Yes, that's the original aux PCB.

Check 8B as it looks loose in the socket. If you haven't reseated the aux PCB ribbon cable, both sides, do so but be gentle. This sounds like an intermittent connection issue. Have you pulled, cleaned, and reseated the PROMs?

Scott C.

 

[yourbestscott]

Yes, that's the original aux PCB.

Check 8B as it looks loose in the socket. If you haven't reseated the aux PCB ribbon cable, both sides, do so but be gentle. This sounds like an intermittent connection issue. Have you pulled, cleaned, and reseated the PROMs?

Scott C.

I reseated 8B. I also pulled 8A and the legs are very corroded. I used a small wire brush I have and cleaned them up a bit but I would need something a little more aggressive.



I had reseated the aux PCB ribbon cable on the board side, but not on the Aux side. However, and this is my fault, when pulling it off this most recent time I bent the pins, and trying to bend the last one back it snapped off. So I'm going to have to order a new cable.

I have not touched many of the chips.

The aux board has been pulled before prior to me. The top of the PROM U5 is cracked.



I tried the trick I've read on here before about putting the Z80A in the slot where the ribbon cable went into to isolate the issue between the boards and I'm just getting static garbage on the screen with no sound.



Sounds like I am tracing down a connection issue at this point. I'm going to have to get some Deoxit and pull all the chips. 8A is concerning to me. It really doesn't look like it's in great shape.

I really can't believe I broke the pin on the cable, that'll set me back some time to test more.

 

[Scott C]

That chip in U5 isn't likely an issue. Replace the cable and report back.

Scott C.

 

[yourbestscott]

That chip in U5 isn't likely an issue. Replace the cable and report back.

Scott C.

Fortunately, nothing's gotten worse since installing a new cable. Unfortunately, nothing's gotten better either

 

[mecha]

if you put the Z80 in the CPU socket (as opposed to the daughter board ribbon cable) and the game doesn't boot then either your Z80 is bad or you have a fault of some kind in the row 6 roms. (which is the 4 mask roms near the CPU socket)

these mask roms can get corrosion on the legs like the small sound PROMs. in which case if the legs have been exposed to said corrosion too long, they can just break off. or possibly the sockets have broken off pins inside. I would encourage removing these 4 roms, and you alternate between sides, you don't pull them out one sided otherwise this will put a lot of stress on those fragile legs and bend them a lot. ensure also while you have them out that the legs don't have 45 degree bends, they need to be straight like |||||| in those single wipe sockets.

then see if the game works with the Z80 installed in the CPU board directly.

 

[Scott C]

As @mecha said, swapping in the Z80 is your next step. It will tell us a lot.

Scott C.