Monstermug
Active member
Got two pac man boards to fix.
Both reported dead.
The first one was an easy fix. Powered up the first board and it was constantly reseting. Dip switch 8 was set to on (which pauses the game) so turning this off allowed it to boot. Game ran fine except no sound. Found that the ram @ 2K was faulty so I replaced it with another DM74S289N and that fixed the sound. Now having a working board will make life exponentially more easier as I can just swap roms and customs IC's around without the downtime.
Second board was more of a hassle.
The reset line on this board was constantly pulsing on power up and the start up sequence did not go through. First thing I did was to verify the both program and gfx roms and found two were bad. I burnt two new roms using 2532 eproms @ 5E and 6F.
Using a logic probe, I probed data and address lines of eproms and found that some pins were floating. First I thought they were just bad sockets but it seems that the floating pins were on the same bus. I discovered that there was a break in the track so I had to add some trace lines to repair the signal. This was easier than desoldering the sockets to do an invisible repair. (there were already trace repairs to this pcb already so I did not see the point)
When switched on I got garbage on the screen. A constant flashing mass of dots with some occasional pac man ghost images appearing on the screen.
At this point the Z80 CPU was not reseting. Probing the Roms again I found that Custom IC @ 6D had no data on DB3. I went on to get the schematics online to figure out what the problem is. I traced this signal down the bus to a 74LS367 @ 8D. Pins 11 and Pins 12 was held low. This in turn comes from the dip switch position 4. So I switched the dip switch 4 from On to Off and the game powered up and ran fine! Switching back up to "On" state caused the game not to boot.
Only one thing that could be! A bad 74LS367 @ 8D.
I pulled this out
and replaced with a new 367
and the game now runs fine. Had a few games and let it run for an hour and determined that it was now fixed.
So if your pac man seems to not be able to boot, make sure dip 8 is switched off and try switching the other dips to on and off on at a time! If that fixes the problem it's most likely the row of 367's on row 8.
Both reported dead.
The first one was an easy fix. Powered up the first board and it was constantly reseting. Dip switch 8 was set to on (which pauses the game) so turning this off allowed it to boot. Game ran fine except no sound. Found that the ram @ 2K was faulty so I replaced it with another DM74S289N and that fixed the sound. Now having a working board will make life exponentially more easier as I can just swap roms and customs IC's around without the downtime.
Second board was more of a hassle.
The reset line on this board was constantly pulsing on power up and the start up sequence did not go through. First thing I did was to verify the both program and gfx roms and found two were bad. I burnt two new roms using 2532 eproms @ 5E and 6F.
Using a logic probe, I probed data and address lines of eproms and found that some pins were floating. First I thought they were just bad sockets but it seems that the floating pins were on the same bus. I discovered that there was a break in the track so I had to add some trace lines to repair the signal. This was easier than desoldering the sockets to do an invisible repair. (there were already trace repairs to this pcb already so I did not see the point)
When switched on I got garbage on the screen. A constant flashing mass of dots with some occasional pac man ghost images appearing on the screen.
At this point the Z80 CPU was not reseting. Probing the Roms again I found that Custom IC @ 6D had no data on DB3. I went on to get the schematics online to figure out what the problem is. I traced this signal down the bus to a 74LS367 @ 8D. Pins 11 and Pins 12 was held low. This in turn comes from the dip switch position 4. So I switched the dip switch 4 from On to Off and the game powered up and ran fine! Switching back up to "On" state caused the game not to boot.
Only one thing that could be! A bad 74LS367 @ 8D.
I pulled this out
and replaced with a new 367
and the game now runs fine. Had a few games and let it run for an hour and determined that it was now fixed.
So if your pac man seems to not be able to boot, make sure dip 8 is switched off and try switching the other dips to on and off on at a time! If that fixes the problem it's most likely the row of 367's on row 8.
