Game: Original Bally/Midway Pac-Man pcb.
Purchase Description: Non-Working/Parts and Repair.
Fault on Receipt: Missing 5F prom/eprom, missing 3x Bi-Polar Proms, no custom IC’s/daughter cards and no Z80 CPU. Unable to test “as is”.
I recently picked up another Pac-Man board that needed bringing back to life. This board has some previous repair work in the past, the 161 counter at 9C had been replaced and somebody had replaced the daughter card sockets at 6D and 5S with some sort of heavy duty Bakelite industrial style 28 pin sockets (N.B., at the time of taking the photo I had already starting removing some of the socketed roms)…
Sadly, the back of the pcb doesn’t look so great. The most noticeable thing is some black paint spillage on the board and the soldering job underneath to these chunky sockets is pretty poor. There is track damage to these replacement sockets and it all looks a bit ugly. Sorting the damage out and replacing them with standard dual wipe sockets will certainly be my first task.
On the plus side, the 6x 2114 rams are all working and the 5x proms/eproms that were still in the board are good too. The 6F eprom has been fitted with the fast Pac hack.
With a couple of replacements sockets fitted to 6D and 5S (along with the various track repair work and every connection beeped out for continuity with the DMM), replacement V-Ram Addresser and Sync Buss daughter cards fitted, a new eprom burnt for 5F, a new Z80 processor and 3x Bi-Polar proms borrowed from another Pac-Man board…It was time to fire this board up.
This is what I was greeted with on my first power up…
Clock on pin 6 to the Z80 is fine, however the game is watch-dogging (Z80 pin 26 not staying high).
First thoughts are there’s an issue with either the Sync Buss Controller (the track damage underneath the socket was definitely the worse of the two, so I wondered if there’s still a broken track or something), the Z80 is perhaps faulty, maybe a problem with the program roms or perhaps there’s a timing issue with the 161 counters around the 3R/3S/2R/2S area .
I was pretty thorough beeping out the connections to the Sync Buss socket, the Z80 is brand new (and previously testing working) and the game roms are a complete set from another working board, so I head straight to the first counter at 3R. Audible outputs on logic probe seemed slightly weak to the ear, so I thought I’d take a closer look using the SLICE kit.
The thing I’ve found with using SLICE on Pac-Man’s counters in the 2R/2S/3R/3S area is that it always fails on the 2R,2S and 3S counters, however the first counter at 3R always passes fine. In this case however, it threw up errors on the 3R counter…
I’m going to take it that the chip is bad (it’s a Signetics branded type), so I replace the chip with a brand new one (ironically also a Signetics). It makes no difference, I’m still greeted with the same non-booting screen. I test both Signetics chips in my tester, they both pass. I leave the new socketed chip and move on.
I’m now thinking there’s perhaps a dodgy socket issue somewhere (more than likely the 4 program roms in row 6). With the exception of the two daughter card sockets, every other socket is still the original Midway ones. I remove the Sync Buss controller daughter card and beep out every connection to every pin on the 4 game roms. I discover there’s no connection to pin 22 of the rom at 6E (the A9 address line)…
There’s continuity underneath the board to pin 22, however contact is not getting to the eprom chip leg, so the socket must be faulty. I replace the socket but the game is still not work and still showing the same boot up garbage screen.
Boot up garbage is also a sign of bad ram. I know my ram is good, so I check all the socket connections to all 6x 2114 rams, they are all fine.
I’m thinking, maybe somehow I’ve been unlucky and one or more ram has just suddenly died. So I remove all 6 rams from another good working Pac-Man, plus the V-Ram Addresser, and for good measure, I borrow the Texas Instruments 161 logic chip at 3R as well (which was already factory socketed on this other Pac-Man). I fit everything onto this Pac-Man board, and it fires right up and is working great!
I swop the removed parts over onto the other known good working Pac-Man board and now this other board is showing a garbage boot-up screen! At least I’ve narrowed down the potential issue/s. I start swopping parts between both Pac-Man pcbs to try and isolate the problem and now both boards are not working
I notice that one of the legs to the borrowed Texas Instruments 74LS161 chip broke off, so I fit a new replacement 74LS161 from stock, yet another Signetics branded chip.
Now both boards are not working and both are booting to garbage
The only real change I’ve done since swopping parts between the two boards is to replace the 74LS161. It worked great before the TI chip leg broke, but not at all trying 3 different Signetics chips. The only other 161’s I’ve got in stock are some Chinese branded HLF chips, I know they work fine so I pull the Signetics in both boards at 3R and fit the HLF’s instead, both boards now work perfectly
I’m guessing there’s an issue with Pac-Man boards and certain branded chips being used at 3R. The other counters at 2R, 2S and 3S are all Signetics and have the same batch code as the original one I pulled.
Looking through my other Pac-Man pcbs, I note I’ve got three other boards that have Signetics chips at 2R/2S/3S but a different branded socketed chip at 3R (usually a Texas Instruments). Also, 3R is sometimes factory socketed so I’m thinking perhaps this was an issue that Midway knew about.
At least I can now say that Pac-Man board number 4 is now fixed. I intend to get this board hooked up to a reproduction EPOS AUX pcb so I can give The Glob/Beastie Feastie a try
Summary
Fitted new Z80.
Fitted and burnt a new HN462532G Eprom at 5F.
Fitted reproduction 284 Video Ram Addresser custom pcb.
Fitted reproduction 285 Z80 Sync Buss Controller custom pcb.
Replaced 28 pin socket at 6E due to connection issue.
Replaced Signetics Branded 74LS161 at 3R causing non-booting garbage graphics.
Replaced 2x 28 pin sockets for daughter cards and repaired broken tracks.
Fitted 3x Bi-Polar proms: 1M and 3M for sound, 4A for colour.
Parts needed for this repair
Replacement 284 V-Ram Addresser daughter board
Replacement 285 Sync Buss Controller daughter board
1x Z80 CPU chip
1x HN462532G Eprom
1x 74LS161 chip
3x 82N129N Bi-Polar Proms
Purchase Description: Non-Working/Parts and Repair.
Fault on Receipt: Missing 5F prom/eprom, missing 3x Bi-Polar Proms, no custom IC’s/daughter cards and no Z80 CPU. Unable to test “as is”.
I recently picked up another Pac-Man board that needed bringing back to life. This board has some previous repair work in the past, the 161 counter at 9C had been replaced and somebody had replaced the daughter card sockets at 6D and 5S with some sort of heavy duty Bakelite industrial style 28 pin sockets (N.B., at the time of taking the photo I had already starting removing some of the socketed roms)…
Sadly, the back of the pcb doesn’t look so great. The most noticeable thing is some black paint spillage on the board and the soldering job underneath to these chunky sockets is pretty poor. There is track damage to these replacement sockets and it all looks a bit ugly. Sorting the damage out and replacing them with standard dual wipe sockets will certainly be my first task.
On the plus side, the 6x 2114 rams are all working and the 5x proms/eproms that were still in the board are good too. The 6F eprom has been fitted with the fast Pac hack.
With a couple of replacements sockets fitted to 6D and 5S (along with the various track repair work and every connection beeped out for continuity with the DMM), replacement V-Ram Addresser and Sync Buss daughter cards fitted, a new eprom burnt for 5F, a new Z80 processor and 3x Bi-Polar proms borrowed from another Pac-Man board…It was time to fire this board up.
This is what I was greeted with on my first power up…
Clock on pin 6 to the Z80 is fine, however the game is watch-dogging (Z80 pin 26 not staying high).
First thoughts are there’s an issue with either the Sync Buss Controller (the track damage underneath the socket was definitely the worse of the two, so I wondered if there’s still a broken track or something), the Z80 is perhaps faulty, maybe a problem with the program roms or perhaps there’s a timing issue with the 161 counters around the 3R/3S/2R/2S area .
I was pretty thorough beeping out the connections to the Sync Buss socket, the Z80 is brand new (and previously testing working) and the game roms are a complete set from another working board, so I head straight to the first counter at 3R. Audible outputs on logic probe seemed slightly weak to the ear, so I thought I’d take a closer look using the SLICE kit.
The thing I’ve found with using SLICE on Pac-Man’s counters in the 2R/2S/3R/3S area is that it always fails on the 2R,2S and 3S counters, however the first counter at 3R always passes fine. In this case however, it threw up errors on the 3R counter…
I’m going to take it that the chip is bad (it’s a Signetics branded type), so I replace the chip with a brand new one (ironically also a Signetics). It makes no difference, I’m still greeted with the same non-booting screen. I test both Signetics chips in my tester, they both pass. I leave the new socketed chip and move on.
I’m now thinking there’s perhaps a dodgy socket issue somewhere (more than likely the 4 program roms in row 6). With the exception of the two daughter card sockets, every other socket is still the original Midway ones. I remove the Sync Buss controller daughter card and beep out every connection to every pin on the 4 game roms. I discover there’s no connection to pin 22 of the rom at 6E (the A9 address line)…
There’s continuity underneath the board to pin 22, however contact is not getting to the eprom chip leg, so the socket must be faulty. I replace the socket but the game is still not work and still showing the same boot up garbage screen.
Boot up garbage is also a sign of bad ram. I know my ram is good, so I check all the socket connections to all 6x 2114 rams, they are all fine.
I’m thinking, maybe somehow I’ve been unlucky and one or more ram has just suddenly died. So I remove all 6 rams from another good working Pac-Man, plus the V-Ram Addresser, and for good measure, I borrow the Texas Instruments 161 logic chip at 3R as well (which was already factory socketed on this other Pac-Man). I fit everything onto this Pac-Man board, and it fires right up and is working great!
I swop the removed parts over onto the other known good working Pac-Man board and now this other board is showing a garbage boot-up screen! At least I’ve narrowed down the potential issue/s. I start swopping parts between both Pac-Man pcbs to try and isolate the problem and now both boards are not working
I notice that one of the legs to the borrowed Texas Instruments 74LS161 chip broke off, so I fit a new replacement 74LS161 from stock, yet another Signetics branded chip.Now both boards are not working and both are booting to garbage
The only real change I’ve done since swopping parts between the two boards is to replace the 74LS161. It worked great before the TI chip leg broke, but not at all trying 3 different Signetics chips. The only other 161’s I’ve got in stock are some Chinese branded HLF chips, I know they work fine so I pull the Signetics in both boards at 3R and fit the HLF’s instead, both boards now work perfectly
I’m guessing there’s an issue with Pac-Man boards and certain branded chips being used at 3R. The other counters at 2R, 2S and 3S are all Signetics and have the same batch code as the original one I pulled.
Looking through my other Pac-Man pcbs, I note I’ve got three other boards that have Signetics chips at 2R/2S/3S but a different branded socketed chip at 3R (usually a Texas Instruments). Also, 3R is sometimes factory socketed so I’m thinking perhaps this was an issue that Midway knew about.
At least I can now say that Pac-Man board number 4 is now fixed. I intend to get this board hooked up to a reproduction EPOS AUX pcb so I can give The Glob/Beastie Feastie a try
Summary
Fitted new Z80.
Fitted and burnt a new HN462532G Eprom at 5F.
Fitted reproduction 284 Video Ram Addresser custom pcb.
Fitted reproduction 285 Z80 Sync Buss Controller custom pcb.
Replaced 28 pin socket at 6E due to connection issue.
Replaced Signetics Branded 74LS161 at 3R causing non-booting garbage graphics.
Replaced 2x 28 pin sockets for daughter cards and repaired broken tracks.
Fitted 3x Bi-Polar proms: 1M and 3M for sound, 4A for colour.
Parts needed for this repair
Replacement 284 V-Ram Addresser daughter board
Replacement 285 Sync Buss Controller daughter board
1x Z80 CPU chip
1x HN462532G Eprom
1x 74LS161 chip
3x 82N129N Bi-Polar Proms
