Help with Pac problem

don1400

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Up until about 10 days ago I had a working Pacman, but after I took the board out so I could test a 4 in 1 mod I did on a friends board Murphy's law kicked in. Just swapped boards to test my wiring of the 4 in 1, played a few rounds and reinstalled my board only to find it not working. I've checked Mowerman's site, Mike's Arcade and I did see something similiar to my boards symptoms on Arcadegame over pix concerning video RAM, also checked out Trouble Shooting Logic board repair manual. Here's the limited things I've done to try to find problem, checked ROM checksums, swapped all video RAMS with known good ones, good Z80, sockets on the Z80, sync buss controller & V RAM cards replaced several years ago.

You can take a look at what game is doing and take a listen to the audio (constant pulsing sound) here: http://www.youtube.com/watch?v=gibRPvwiZ70

Note: vid runs about 25 sec, the entire sequence ends with the screen showing zeros and green dots plus no audio pulses, at this point the game will stay on that screen till it is unplugged and powered up again.
Any Pac experts have any thoughts on this problem?
Thanks,
Rich
 
Im at work and cant look at youtube videos here. I will check it out when I get home this evening and see if i can help.
 
Sounds like it's stuck with a watchdog reset.

Reseat the socketed chips and make sure the daughter boards are seated well.

RJ
 
Yes its watchdogging, the programs not running. Start looking around row 6, check the back of the pcb and make sure no leads got shorted while the board was out.
Verify your +5v across C3 too just to be sure. Did you remove the dughtercards?...make sure they were plugged in properly.
 
Yes its watchdogging, the programs not running. Start looking around row 6, check the back of the pcb and make sure no leads got shorted while the board was out.
Verify your +5v across C3 too just to be sure. Did you remove the dughtercards?...make sure they were plugged in properly.

I checked all the pins in row 6, nothing touching other pins or traces, checked continuity on the eprom pinouts and the sync buss controller, all pinouts are going where they should so there aren't any broken traces. Voltage on C3 is 4.8v. Daughter cards were tied down, I pulled the cable ties off and reseated both cards, board still doing what you saw in the video. Any other thoughts on the problem?
Thanks,
Rich
 
The problem is this could be caused by many many different things so its not something you can really troubleshoot here. If you have a spare 74LS161 you can try piggybacking 9C and see if it will boot. Really not much else I can suggest unless you have a logic probe there.
Meter the 4 fuses in the bottom of the cab. Even though you have 5v you might have one fuse dead. Have the fuse holders been replaced before?
 
those fuse holders down there by the transformers are a source of many problems. kinda funny that it would start now but if you like checking potential problems off the list then i would replace those.
then i would look at the pins inside the connector. they get weak over time and dont grip the PCB tight enough to allow for proper electron flow/game operation. look inside the connector real careful like and see if the pins are oxidized, or is the spacing the same with them all? is there dirt in there? anything obvious wrong in there? finger edge contacts clean? some replace the connector, i replace the pins inside there at any hint of problems.

you can test to see if you are getting the right voltages on the PCB. look here:

http://web.archive.org/web/20050228090057/http://users.erols.com/mowerman/pacfile.htm

also look here for info on how to test the connector if you dont know how. its not a pac man board but the concept is the same. just be careful with the pac man board as you have AC going into the board and its converted to useable voltages on the PCB. just check out the edge connector pinout on the above site so you know what to set your multimeter at.

http://www.elektronforge.com/testedgeconn.htm
 
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Thanks for the help, slow to reply, computer took a dump. I pretty much tried to bullet proof game several years ago, replaced fuse block, cap kit rewired all pins in AMP connectors, put Bob Roberts PCB edge repair kit on the board as well as replacing the edge connector. Didn't put in a switching supply, wanted to keep it all original. I
piggy backed a 161 at 9c as suggested by Riptor, no change. A Ms Pac and spare Pac board all work in the game so that suggests the problem is with the board, it's just one of those frustrating things we all love about this hobby. I've got a Berzerk that needs attention right now so the Pac board goes on the back burner.
Again thanks for the help.
Rich
 
Thanks for the help, slow to reply, computer took a dump. I pretty much tried to bullet proof game several years ago, replaced fuse block, cap kit rewired all pins in AMP connectors, put Bob Roberts PCB edge repair kit on the board as well as replacing the edge connector. Didn't put in a switching supply, wanted to keep it all original. I
piggy backed a 161 at 9c as suggested by Riptor, no change. A Ms Pac and spare Pac board all work in the game so that suggests the problem is with the board, it's just one of those frustrating things we all love about this hobby. I've got a Berzerk that needs attention right now so the Pac board goes on the back burner.
Again thanks for the help.
Rich

Replace your sockets. My Ms. Pac used to do that, the sockets for the satellite cards felt a little weak, so I replaced those and while I was at it replaced all the other sockets as well. Not sure which socket fixed it, but after I changed them all out, she fired right up.

Worth a shot, only costs a couple of bucks and about an hour of time (I work slow... sue me).
 
That's exactly what I'm gonna do, at the very least I should have replaced sockets for the daughter cards automatically when I was upgrading the other parts.
Thanks,
Rich
 
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