pacman is posessed

supercharged

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My pacman works fine as soon as I trun it on; after a few minutes I can walk back over to it and it scrambles the screen when I put a quarter in it and doesn't give a credit???

Occasionally the sound goes out also

A real ghost in the machine??
 
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I would start by checking the voltages on the board after it has warmed up. Also make sure that the edge connector is clean (i.e. not corroded) and the wiring harness connector pins are in good shape.
 
My pacman works fine as soon as I trun it on; after a few minutes I can walk back over to it and it scrambles the screen when I put a quarter in it and doesn't give a credit???

Occasionally the sound goes out also

A real ghost in the machine??

Well, the reset is probably due to a static charge. Very common in the Bally/Midway games. My solution is to not allow shoes in the game room.

Sound going out, could be Caps on the board.
 
LONG before replacing caps I would clean the edge connector on the board... check it for signs of burning/scorching/discoloration from heat. Replace the edge connector if that's the case.

Next up: Replace the original fuse holders with ones from Radio Shack. The fuse holders in that game are known sources of problems.

Once those are knocked out as not the cause then move on to other things.

Oh, and ground the coin door properly.
 
Power issue. Which is on the PCB. Off the top of my head I would be looking at caps.

Maybe it time for a Bob roberts Ms pac man cap kit..

That if after you cleaned the edge connector and are still having issues..
 
Power issue. Which is on the PCB. Off the top of my head I would be looking at caps.

Maybe it time for a Bob roberts Ms pac man cap kit..

That if after you cleaned the edge connector and are still having issues..

I totally disagree.

Pac cabs have brass fuse holders that loosen up and corrode. Over time these cause power issues and should be addressed BEFORE you go spending time replacing caps.

Same thing for the edge connectors. They burn up long before you need to replace caps. Check them and clean the edge connector first before replacing caps.

And if you have a filter board between the harness and the game board, get rid of it. It's another cause of power issues.

Do those things before you start soldering on the board.
 
I agree, its actually pretty rare for a pac to have bad caps with the exception of the sound circuit. It is not uncommon to find the 2200uf and 330uf caps bad.
Your resetting problem is likely a power issue and as Raymond said check the fuse block FIRST. If it has the original fuse block replace it regardless of its condition. They used brass contacts and brass fatigues and looses its spring and also cracks very easily. Of course you should ohm out all 4 fuses while your at it. I have seen boards run with just one good fuse.
Clean the edge connector on the board with some #000 steel wool or a fiberglass scratch brush, NOT sandpaper. I use a scratch brush. It will remove the oxidation with a few light strokes.
 
I totally disagree.

Channelmanic has a point but before changing fuses holder or mucking with the edge connector. Check if you got 5 volts across C2 or C3

If you want to see if the fuses holder is your issue just a few small plastic cloth pins will tell you really quick if it is an issue.

an upside down can of air will give you the ability to cool off parts and see if you can isolate the problem.
 
Thanks guys,

Always great information. I have already cleaned the edge connector as I learned that lesson from a burnt one on a MS. Pac that I had to replace!

I will replace the fuse block regardless and make sure the coin door is properly grounded.

I also considered wiring in a modern power supply for reliability.

I will replace the caps in the sound circuit but i do not have a wiring schematic so a pic of them on the board would be of great help.

Thansk again
 
The pacman power supply is pretty bulletproof once the fuse block is replaced and the edge connector cleaned/repaired.
The two most critical caps in the sound section are the big ones right next to the smaller heatsink. There is also a 4.7uf one tucked under that heatsink that tends to dry up from the heat.
 
Bob roberts site does have a cap kit it's about 7.50

http://www.therealbobroberts.net/mpcaps.html

Yes, the design of the Ms pacman boards is stable once you fuse holders. Yes the Caps on the board fail less then the ones in power supply or monitors.

Now how old are these caps and how much longer are you expecting them to last or expect them to be available?
 
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