Ms Pac sync bus control question

shirkle

Active member
Joined
Jan 6, 2003
Messages
1,612
Reaction score
5
Location
Virginia
Today, I went to try to fix someone's Ms. Pac. I turned it on and got garbage on the screen. Pull out the board, and I noticed a chip at location 6D is horribly dirty. I pull the chip and just reseat it...plug it back in and it works.
So, I figure I better do the job right and really clean that chip...pulling it out the second time, however, left 3 legs behind...none of which could be soldered back on.

So, I know this chip is the problem, and I leave thinking I'll just order one and it should work.

Later, I realized that location 6D is where the sync bus controller goes. The chip was old looking...old enough to be very dirty and coroded. What chip was this? Can I still use a regular sync bus controller board there? I have one handy(from a Pac-Man board) and I'll use it if it'll work there.

5D was also just a chip, and this is where the VRAM addresser usually is. This chip was also extremely diry and old looking. Also, there was no daughter board. It was an original board though....just missing the usually parts.

By the way, the game had an "Eldorado" tag on it. :/
 
I know that jrok.com had built a single chip that could be used to repace bad sync bus or vram boards... Sounds like thats what you have...
 
I know he did too, but this chip was old and unlabeled, so I assumed it was something else. I can't imagine something new from jrok already being corroded....especially in a rarely used, completely restored game in someone's finished basement.

Should a plain old regular sync bus board still work then if I swap it over?

EDIT: I just looked up a picture of jrok's....these were definitely not from there. These looked like plain old chips...just black chips with nothing written on them.
 
Should a plain old regular sync bus board still work then if I swap it over?


Yes.

Early runs of pac boards had custom IC's instead of the cards for the Sync controller and VRAM add. The story goes (short version) that not enough of the customs could be supplied to keep up with demand, so cards using standard off the shelf IC's were created.

The custom's and cards are interchangeable.


D
 
Well...I just tried it and it didn't work! I'm going to go with soldering the legs of the original chip back on for now.

Did those original custom ICs take the place of the daughter card as well? This Ms. Pac has auxilary card/ribbon cable.
 
The Sync and Vram cards are functionally identical to the Sync and Vram custom IC's, if swapping out the customs for the cards didn't fix your problem, then your problem lies elsewhere.

The Sync and Vram cards as well as the customs are the same between Pac and Ms. Pac, they aren't specific to Ms Pac and don't have anything to do with the Ms Pac daughter card.

I just re-read your first post, you mention 5D and 6D, but the customs/cards would be installed in 5S and 6D ??


Does the board seem like it's running at all, or just static garbage on the screen? Have you pulled the ribbon cable and dropped a Z80 back onto the mainboard and rechecked to eliminate the Ms. Pac daughter board?



D
 
Zoot...thanks for the help.

You mentioned the ribbon cable and daughter card, but there isn't one....and it played Ms Pac without it!
In my original post, I meant 5S...I just accidentally typed 5D.

Anyway, I had the game working briefly, as it was, prior to breaking a few legs off of the chip at 6D. I replaced 6D with a working Sync Bus card and it didn't work. If I remember correctly, it displayed either all Bs, all Os, or 4 white Ms. Pacmans.

So, I've resoldered the legs back on and I'm going to try it tonight. It should make it work again since it worked prior to breaking the legs.

If not, who knows.

I have the feeling that the board was hacked pretty bad to run Ms Pac. It has wires jumped all over the back of the board.
 
You might need to replace the socket on the board too. It's probably a single leaf type, which when they get old the contacts bend then never spring back.

- James
 
I know that jrok.com had built a single chip that could be used to repace bad sync bus or vram boards... Sounds like thats what you have...

The VRA and SBC daughtercards were apparently made when NAMCO couldn't supply enough NVC284 and NVC285 custom chips for all the pacman boards that were being sold. They had the same crappy silver legs that midways masked roms of that ERA did, so they're renowned for losing corroded legs.

You can replace the parlyzed chip with any of the aftermarket replacement chips/boards.
 
Sounds like you have the hack that runs mspac without the daughterboard. Its not that hard to put it back to original but if you get it working I would just leave it be. I agree, your issue may be just a socket. At least it was before you broke the legs off the chip.
 
I know that jrok.com had built a single chip that could be used to repace bad sync bus or vram boards... Sounds like thats what you have...

The VRA and SBC daughtercards were apparently made when NAMCO couldn't supply enough NVC284 and NVC285 custom chips for all the pacman boards that were being sold. They had the same crappy silver legs that midways masked roms of that ERA did, so they're renowned for losing corroded legs.

You can replace the parlyzed chip with any of the aftermarket replacement chips/boards.

I think I remember reading the same thing in the logic troubleshooting manual.
 
Back
Top Bottom