Ms Pacman PCB Problems

crazykong72

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Hi,

I'm new to these forums, but am hoping somebody can help me.

I'm over in the UK and have a cocktail Ms Pacman with what looks like a geniune Midway unmodded PCB. Problem is the machine has run fine for years, but since moving it, the following has happened.

The graphics are corrupt, more specifically the score line is show in reverse vertically left of middle. The maze also wobbles and looks corrupted, kinda transposed 2 or 3 times in the wrong postion. It is very similar to this fault on Pacman here. The main difference is that the screen is a bit more garbled and sometimes fixes itself and then goes wrong again...

http://www.mikesarcade.com/arcade/images/pacpix/pacprob-squares.jpg

I've ruled out the monitor being at fault, as the boot up is displayed fine until the cross hair grid appears.

I've taken a look at the board in situ, and it seems to be an untouched Midway board, with MsPac daughter board, the VRAM 284 card, and the Sync Buss 285 card.

First point of call was to remove both the 284 and 285 card, brush with toothbrush, and reseat them. This did not appear to have any effect.

Next tried looking for chip A8, as suggested at Mikes Arcade, it is at the far right from the P1 control panel. Looked at the feet of this, and they dont seem corroded. Gently touched it to see if it was a contact problem, nothing.

Next I removed the edge connector off the PCB loom to see if was a problem here. Again nothing.

After pulling the board out of the machine and visually inspecting it, giving it a slight clean and refitting it, the problem is still there.

The only thing I have spotted is that around the A8 area, some of the green board layer has come away. I will take a close up photo of this later and show it.

Currently I've attached some pics of the problem, and upload a vid a youtube here:

http://www.youtube.com/watch?v=Zu7x3cjsnc0

I'm a newbie with no prior board repair experience, dont have a logic probe, but can use mulitmeter and solder.

Any thoughts or help would be most welcome.

Thanks.
 

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Bad VRAM addresser / VRAM addresser socket.

That would be a good place to start. Since the problem happened when you moved the machine it probably just needs to be reseatted. You might have a socket crapping out on you too which is very likely since they used crappy sockets on these. Have someone watch the screen and wiggle the daughtercards slightly and watch for change. You might have to pull the card and lightly scrape the legs if they have corrosion on them.
 
Thanks for the advice so far.

Pulled the 284/285 (they both have no rust and are clean) and reseated them, no change. Wobbled them whilst plugged in and again, no change. The 285 clip strap thing has been cut in the past, so maybe this has been replaced in the past.

Could the VRAM be dead/dying? It still sometimes very briefly sorts itself out and looks normal without touching the PCBs, then the glitches start to return again a few seconds later.

Any other things I should check with a multimeter?

Thanks
 
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Thanks for the advice so far.

Pulled the 284/285 and reseated them, no change. Wobbled them whilst plugged in and again, no change.

Could the VRAM be dead/dying? It still sometimes very briefly sorts itself out and looks normal, then the glitches start to return again a few seconds later.

Any other things I should check with a multimeter?

Thanks


The daughterdcards dont usually go bad unless they are plugged in backwards. Other than that they do suffer from bad connections but its the sockets fault. I replace these two sockets no matter if the board is working or not.
Check your +5 on the board and inspect your edge connector.
 
The daughterdcards dont usually go bad unless they are plugged in backwards. Other than that they do suffer from bad connections but its the sockets fault. I replace these two sockets no matter if the board is working or not.
Check your +5 on the board and inspect your edge connector.

Thanks for the tip. Sorry about delay, but only had a chance to pull the board out of the machine to check today.

OK, +5 pins are giving a reading of around 4.9v, so guessing this is not a problem tolerance level. The edge connector looks like it is in pretty good shape, bit dirty but after cleaning looks VGC, apart from a slight bit of burn on A/1 pins which seems quite common, but main point is it makes good contact with the harness.

Pull and reseated all removeable chips, that were storing nearly 30 years worth of dust and dirt, but very little rust.

Switched it back on and it's still not working. I'm still thinking something must have got jolted when moving the machine, but having wiggled and pressed every component on the board, with no change in output, I'm a bit lost at what it could be.

The thing that gets me is sometimes when it warms up, for a about a minute, the screen starts to look OK and cured, but then it soon descends back into the multi-draw, static, vertical text output as before.

Any more advice, or should start looking for a replacement board, or a course in PCB board repair?
 
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Pull the vram card out and inspect the pins very closely. Sometimes a pin will corrode off on those yellow sockets. You might have a bad socket as well. Whatever is causing it, shouldnt be too hard of a fix.
 
I had a board that looked similar to that repaired by hyperspace arcade and I believe he said it was a bad trace on the vram. It was split down the center of the screen with the maze repeated twice and none of that static stuff.
 
OK thanks for the input guys. Back to looking at the VRAM board it is then. I'll pull it out remove the yellowy brown socket holder in between the board and the VRAM chip pins, examine and take some photos, post them and report back later.
 
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Crazykongfan - Crazy Kong was the only Kong game available in England in 80s apart from a few Nintendo cabs; hence the name, like yours too.

OK, thanks all for the help so far, this Ms Pac is starting to make my head hurt. I've pulled the VRAM again, taken the yellow/brown interconnection off, cleaned it, put back in the socket and the problem is still there.

Here's a pic of the VRAM removed, as you can see none of the pins are bent or missing, and there's no rust, so is there anything else I could try like getting a new VRAM, or do I need to get a pro to look at the board.
 

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Something I have seen on quite a few of these daughtercards is that under the yellow socket you fill find cut traces on the pcb. Its caused by people using whatever to pry the yellow socket off. Check that out and see what you find. Sometimes its just one of the little solder spots that got smeared onto another trace and can be hard to see so check it over real good.
 
Try replacing video chips, there are 3, I think

When I repair pacman board I have a few old parts boards around to fault find with.

Trouble is, I live in Australia, so the freight kills that idea now.

If you are from the states, grap a spare dead board or 2, and do swapping. They are on ebay all the time in the US

Chances are the board will come to life then. I once swapped all chips to a graphiccally crap board, and that fixed it, so I swapped them 1 at a time and found the chip causing it. It was 3A I think

At least now you can safely say the vram addresser is probably OK, so good luck
 
Thanks guys for all the feedback. I've opened the machine up again at the weekend and checked over everything, but cannot see any visible sign of cut traces, dry joints, or bent pins on any of the chips/or VRAM/or Bus Sync. The only area of concern I noticed again was around the A8 chip near the small brown cap where there is a bit of board where the green covering is starting to come away, but no traces seem to be damaged. I'll get a picture of this up soon.

I am located in the UK, so getting hold of spare boards is probably easier than being in Oz, but not as easy as in the States (anyone got a unmodded Midway Pac/Ms Pac board they want to sell and don't mind shipping to the UK?).

Before I go fully down this route though, I want to check the voltages again as I'm not 100% sure that the readings I'm getting are being taken on the right place on the board to read them accurately.

Firstly I notice there are both AC and DC boards, is there an easy way to tell which board type is in this machine (Cocktail Ms Pac)? Silly question, but I'm guessing DC.

Secondly am I doing the right thing by measuring the voltage on the board edge connector accross GND/Earth and +5DC/+7AC multiple pins? Should I be reading it from the harness connector or somewhere on the board instead?

And finally, if the readings I'm getting are too low or too high, is there a way to modify them easily on the PSU?

Thanks again.
 
All Pacs and MsPacs used an AC power supply. Jr Pac is the one that had both AC and DC versions.
Measure your +5 across cap C3. You will get somewhere around 4.9-5.1v typically. There is no adjustment for the +5, if its not right you need to find the defective part and replace.
 
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