Ms. Pac-Man graphics issue

delroy666

Well-known member

Donor 2011
Joined
Jul 30, 2009
Messages
1,189
Reaction score
26
Location
Ottawa, Ontario, Canada
I'm trying to help a co-worker with his Ms. Pac board. The gameplay is fine, sound is fine, but the graphics (maze, dots, text and characters) seem to be 'chopped up' or repeated in places. I've attached some pics to show the problem. It doesn't quite seem to match with any of the pics or descriptions on the various troubleshooting pages on the 'net.

I put the PCB in my known-good Pac-Man cabinet, and the problem persists, so I know it's a PCB issue rather than a monitor issue. I unplugged the ribbon cable to the daughter board and installed Z80 on the main board to make it play as regular Pac-Man, but the graphics still show the same problem. I swapped in the sync bus controller and VRAM addresser from my working Pac-Man PCB but it didn't help either.

I'm looking for some ideas for what to try next. Any suggestions would be appreciated.
 

Attachments

  • IMG_2076.jpg
    IMG_2076.jpg
    54.1 KB · Views: 33
  • IMG_2078.jpg
    IMG_2078.jpg
    46.8 KB · Views: 30
  • IMG_2079.jpg
    IMG_2079.jpg
    45.4 KB · Views: 23
  • IMG_2080.jpg
    IMG_2080.jpg
    76.7 KB · Views: 24
  • IMG_2077.jpg
    IMG_2077.jpg
    44.3 KB · Views: 32
I have this board on my test bench now and have been trying to figure out the graphics issue, so far with no luck. As I mentioned before, the game actually plays perfectly, it just has the weird lines through all the objects. When Ms. Pac and the ghosts are moving vertically, they look normal - when moving horizontally, they get the lines going through them which makes their movement look jittery.

I did find a ROM at U7 that didn't verify, (1 bit different from the MAME ROM image) but burning a new one didn't fix the graphics issue. The Fluke ROM, RAM and bus tests all pass. I've started checking the signals going in/out of the ICs near the video output using a logic probe, and they look okay so far. I also checked the databus DR0-DR7 and nothing appears to be shorted or tied high/low.

Since graphics issue affects all the different objects on the screen (characters, sprites, etc) does that give a clue to where the problem might be?
 
Good call. When I originally read through that page, I didn't recognize my problem being what it describes as "Images and Text are 4 1/4 of the left side of a Sprite repeated." I checked the 74LS283 @ 1F as it suggests and according to my logic probe, all the outputs were toggling nicely. Just for the hell of it though, I piggybacked a new IC on top of it and the graphics cleared right up. I socketed and replaced the 74LS283 @ 1F and the board is working 100% now. Thanks!

:beerchug:
 
Back
Top Bottom