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Pacman PCB Repair


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23/05/2019

 

Pacman PCB bought from @Pelly back in January on AA.

Been a long time since I've done any arcade pcb repairs :(

On first inspection looks like somebody has hacked this pcb to run Ms Pacman, quite a few traces cut.

First thing is to bring the pcb back to original. Fixed all cut traces (roughly 7) and replaced the 4 main program rom sockets (See pics). Burnt a set of Pacman roms on 2532's and surprisingly the board fired straight up with a few issues.

IMAG0081.jpg IMAG0083.jpg

IMAG0084.jpg IMAG0086.jpg

Also removed this 74LS00 that was added in for the hack.

 

Fault: Only clicks for sound.

When starting the game all sound effects and music were just clicking sounds. Since it was trying to produce the sounds I eliminated the amp as an issue and any circuitry that triggers the sounds.

 

Solution: Bad 82s25 ram @ 2k. These can be replaced with 74LS89's or in my case I bought a heap of Russian equivalents years ago 155PY2 which work great and finally came in handy.

 

Fault: After running the board for several hours I could see the characters all had vertical lines in them and were split in half with half of the character at the top and bottom. Eventually all characters were moving in the bottom half of the screen.

IMAG0091.jpg

 

Fix: Found a data line being pulled down DR7 on pin 11 of a 74LS283 @ 2F. This connects to 2 other chips, a 82s25 ram @ 3F pin 11 which is the source and a 74LS161 @ 2E Pin 6.

Any one of these chips could be pulling down the line however my first guess was correct. Replacing the 82s25 @ 3F fixed the issue. I based my guess on the failure of the other ram in the sound circuit.

Untitled-4.jpg IMAG0093.jpg

Pic of the two failed 82s25's replaced

 

Fault: Game started cycling through its test sequence then reset and repeat in a endless loop.

Fix: Hitting the test button BAD C RAM-1 came up which is a 2114 @ 4P. Easy fix.

IMAG0092.jpg IMAG0095.jpg

 

8 hours later the board is still running strong :)

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Cool.. great to see another original PCB up & running..

Q:- where / what ROM's did you burn ??

i found when refurbishing my Midway Pac-Man & repairing a few PCB's as spares

that one of the ROM programs was Not as in my original PCB

i do not know if the ROM's found on the net are an up-date version ?? a fix for the last screen ?

but when i burnt my set i used the 1980 originals ..

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Cool.. great to see another original PCB up & running..

Q:- where / what ROM's did you burn ??

i found when refurbishing my Midway Pac-Man & repairing a few PCB's as spares

that one of the ROM programs was Not as in my original PCB

i do not know if the ROM's found on the net are an up-date version ?? a fix for the last screen ?

but when i burnt my set i used the 1980 originals ..

 

Funny you should mention that I had a lot of trouble finding a working set from the various "emulation" sites, the first set I burnt didn't work. Luckily I had my single rom hack on hand at first (pic from my next repair)

IMAG0096.jpg

This hack is actually pretty useful as it bypasses the chip enable for the roms.

I didn't have access to my computer at home so I found a set HERE

I've also attached the zip to this post.

pacman.zip

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Cheers.. Thank You for the file..

i will check these out with the original's from my 1980 pac-man

& let you know if the same or different.

i can not remember what chip was different, but have the EPROM set aside with sticker & number on it..

i think it would be good to have an original available for restoration purposes..

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Unfortunately none of my 3 pcb had any original roms on them they were all originally Ms Pacman's and Ms Pacman isn't really the best for working on these pcb's I like using the aforementioned single rom hack but I thought it would be nice to have a full set made up for future repairs. The boards may have had roms on them originally but I think a lot of them had bad legs and fell apart....been a long time.

I'm using this board as a spare for my Ms Pacman cab and its running one of those highscore.com high score/multigame kits and its developed a fault where after about 20-30 seconds the game crashes and you get a bunch of FFFFFFF's on the screen.

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i have a high score kit not fitted yet, but it not multi-game

wanted my machine to stay as original as i can..

it still takes quarters :D

i have a mix of original Ms Pac-man & Pac-Man PCB's all still the AC version

along with a large number of original ROM' chips

i hope one day to bring life back to them all

& reading your thread has given me the inspiration to dig them out

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Best thing you can do in my humble opinion is convert them to DC with a switch mode and I don't say this lightly as I'm a purist. I've just seen too many Pacman PCB's with burnt edge connectors to count.
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"yep" & there is a fix that should be done if the edge connector is not burnt

you only need bride the ground / common / CT back at the transformer

that will put the power ground at both ends of the edge connector

i did this to my pac-man after i noted one or two of my spare PCB's had burnt pins

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