Ms Pacman PCB problem?

tkebean

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I'm working on restoring a Ms Pacman cocktail table. I've been able to get mostly everything back up and running, but not everything so here we go....

When I fire up the game, all I see is a white checkered screen, like a big grid with about 1/2" x 1/2" squares. The game also seems to reset every second. The screen goes black and comes back to the grid (very quick) and the game counter on the coin door goes up 1 with every reset or flicker. When I flip the service switch, all I see is basically a rundown of the Dip Switch settings (free play, points to new ms pac, # ms pacs) and then about halfway down the screen a capital 'L' right in the middle and a piece of the fruit at the bottom right. I haven't seen any diagnostic codes that are just the 'L'. Even when on this screen it seems to constantly reset or flicker.

Is this a PCB issue? Has anyone seen this before or have any ideas how to fix it or what the problem might be? Please Help!
 
Is this a PCB issue? Has anyone seen this before or have any ideas how to fix it or what the problem might be? Please Help!

Sounds like the game is watchdogging and never gets past the initial grid screen. Right after that it should start displaying all the sprites, so I'd start poking around the VRAMS and the EPROMS.

Mowerman's page is the source for Pac tech.

http://lawnmowerman.rotheblog.com/
 
I would also check the voltages. Board watchdog circuits can get tripped by low voltages. If you verify that the chips are not receiving +5 vdc you might look into rebuilding the power supply section of the Pac board. Bob Roberts sells a cap kit which would probably be a good start.
 
The 2 wires that are supposed to go to the jam switch are just connected together. I tied them off so I wouldn't have to worry about the door being shut while I'm working on it. What's the best way to test the voltage going to the board and the EEPROMs? I have a multimeter just not 100% on what exactly to test (this part is something I've never done...Only have some experience rewiring cabs and refinishing them, haven't had to get down to the nitty gritty and test voltages). I know how to use the multimeter i just dont know which pins to touch. I'm trying to figure out from the schematics but I 'm new to reading them and trying to learn. Thanks for your help and any feedback is much appreciated.
 
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The 2 wires that are supposed to go to the jam switch are just connected together. I tied them off so I wouldn't have to worry about the door being shut while I'm working on it. What's the best way to test the voltage going to the board and the EEPROMs? I have a multimeter just not 100% on what exactly to test (this part is something I've never done...Only have some experience rewiring cabs and refinishing them, haven't had to get down to the nitty gritty and test voltages). I know how to use the multimeter i just dont know which pins to touch. I'm trying to figure out from the schematics but I 'm new to reading them and trying to learn. Thanks for your help and any feedback is much appreciated.

Slam switch? or interlock switch? If it is the Slam switch, disconnect the wires.
 
The slam switch is open and the interlock switch is wired closed. If I close the slam switch while it's constantly resetting it stops resetting and freezes on the grid screen.
 
With the test switch off I get the grid and with it on I get the dip switch settings. Either way it constantly resets.
 
I've never had to test voltages on mine either, so I can't say where to test at. On my Asteroids, its clearly marked and there are test lugs on the boards, its real easy. Not so on my Ms Pac boards....
 
I've never had to test voltages on mine either, so I can't say where to test at. On my Asteroids, its clearly marked and there are test lugs on the boards, its real easy. Not so on my Ms Pac boards....

Across the axial cap below the Z80's, near the split in the board is a good place.
 
I got some help reading the schematic and what/how to test the voltages on the board from a co-worker so I'll be able to fire it up and test this afternoon. I'll post the results later today.
 
All the chips on the board are getting 4.96-4.98 volts except for one, the chip at 3D, which is getting about 4.32 volts. Could that be the issue? I even tried completely unconnecting the coin door to make sure it wasn't anything to do with that and the problem still exists with it unconnected. I found 2 similar problems on the lawnmower man.rotheblog.com

Similar sounding problem #1

Game resets often, and/or won't boot. (Also causes Clay's Multi-Pac to reset to menu and freeze)

Chip 8B, 74LS368, inspect for cold solder joints or corrosion on pins. (Thanks Jeff)

Similar sounding problem #2

Constant Reset, Shorting Z80 pin 34 to pin 35 will force boot but with corrupt graphics. (PAC 3 board)

2114 Ram at 4M bad (4P on real board).


I tested the chips associated with both of these issues and both are receiving about the right voltage (4.98).



Does anyone have any ideas?
 
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