Ms. Pacman - Distorted Letters and Maze, but plays

ciceroguy

New member
Joined
Oct 18, 2012
Messages
6
Reaction score
0
Location
New York
Hello,

I recently bought a non-working Ms. Pacman and was able to get it partly working by replacing 74LS74 in 8C.

It plays correctly, but the letters and maze are distorted (see attached for intro screen and screen in play). Even the letters for the test mode are distorted and I can't read them.

I already removed the ribbon cable and put the Z80 on the main board to rule that out. Also, the small glass capacitor for C14 was broken in half, so I replaced that with a .1uf 400V that I had. Didn't make a difference. I'm not sure what C14 is supposed to be.

Any ideas on what to check next?

Thanks!

Matt
 

Attachments

  • 2012-10-18 20.47.02.jpg
    2012-10-18 20.47.02.jpg
    91.8 KB · Views: 37
  • 2012-10-18 20.47.14.jpg
    2012-10-18 20.47.14.jpg
    94 KB · Views: 46
Pull the vram addresser board off and check the pins on it.

Thanks for the suggestion. Pins look good and I checked continuity on all of them. Problem is the same.

I did find that there is a clipped wire that was soldered to one of the pins on the top of the board. Not sure why that's there or how it might be related. The prior owner did some mods and I don't think they were done well.

Matt
 

Attachments

  • 2012-10-18 23.27.01.jpg
    2012-10-18 23.27.01.jpg
    102.8 KB · Views: 20
You have some issues. Sync Bus, VRAM, Character ROMS. All are most likely bad sockets replace all 4 sockets and test again.
 
You have some issues. Sync Bus, VRAM, Character ROMS. All are most likely bad sockets replace all 4 sockets and test again.

Its not related to the sync bus. Typical sync bus problems would be not booting or resets. This is typically vram connection problem or character rom/sockets.
 
Its not related to the sync bus. Typical sync bus problems would be not booting or resets. This is typically vram connection problem or character rom/sockets.
The maze and letters are distorted the same way with and without the Ms. Pacman daughter board. I'm probably misunderstanding, but would that likely rule out the character ROMS since 2 different sets have the same problem?

Also, the ghosts and Ms. Pacman are perfect, so it's not an overall video issue. It's something specific with maze and letters. Something that is corrupting data from both ROM sets?

Thanks for the help. I will check the character ROMS tonight.
 
The character/graphic roms are at 5E and 5F on the main PCB. I was having the EXACT same problem with mine, with or without the daughtercard because 5E had a bent pin.
 
Last edited:
Fixed! Works perfect now!

It was 2 bad pins on 5E. They both looked ok until I popped the chip off and then it was obvious.

Thanks everyone.
 
Back
Top Bottom