Spent some time going through the box of broken Pac-Man / Ms. Pac boards we've got kicking around the shop. Seems like some Pac fixes are very straight forward, others I really struggle with and throw them back in the box. I think part of the problem is the how the boards were stored, some were thrown in a box, might have a scratch or two or some rust some ICs.
These days I tend to only work on cleaner boards, ones that haven't had prior repairs as sometimes the prior repair is botched and makes troubleshooting a PITA. Anyway a few tips for Pac repairs:
- Check out the repair logs, there are quite a bit of repairs out there as well as some good resources on repairing these boards, I'm too lazy right now to look them, Google is your friend.
- Check out the two original Midway Pac-man Advance Troubleshooting Manuals, again Google is your friend.
- As always, inspect the board for damage and other prior repairs.
Here's my basic Pac-Man repair procedure, at the last the beginning, the Midway manuals have additional steps:
Pac-Man / Ms. Pac-Man Board Repair Procedure
- See Pac-Man Troubleshooting Manual.
- Always use known working satellite boards, usually replace the sockets for the satellite boards right away as they tend to fail.
- Always use known working roms on main board. I usually just remove the original proms and burn new 2532 eproms. For Ms. Pac-Man, make sure 2532 roms at row 6 are 45ns or faster.
- Check Ms. Pac-Man ribbon cable, they go bad often.
- Test for voltage on large caps, should be 8.0 VDC on these. Test for 5 VDC on boardset.
- Check for clock signals at Z-80 and other test point (per manual).
- Make sure reset signal at Z-80 is high.
After this I go into using the Fluke 9010a to check that the program roms and program rams are working. After that I usually rely on prior repair logs to narrow the problem down if I don't see anything myself. Some of my repairs from over the years, I don't usually note as many bad program roms anymore as I usually replace them first as preventative maintenance, hope this helps:
No Video, Deadish (3/28/17) – Board had fresh set of program roms installed, fairly clean boardset. Voltage was 6.2 VDC on chips, turns out Q6 was shorted together on the back of the board as two traces were touching each other. Replaced Q6 and voltage was back at 5.05 VDC. Clock and reset line checked out okay, used Fluke 9010a to test Roms and Rams, no problems. Noticed reset line was not going low when hit the push button switch near the amplifier. Replacing 74LS161 at 9C fixed this problem, but no change. Visual inspection showed that 4F was installed backwards, replaced it with a known working Prom and the board fired up.
Board booted to Garbage, pretty much all “P” on the screen with other garbage graphics (3/28/17) – Board had fresh set of program roms installed already, replaced the sockets on the Z-80 and V-Ram board, replaced the Z-80 socket for the heck of it.
Roms checked out okay on Fluke 9010a, all 2114 ram tests failed. Swapped rams and found 4R to be bad. Replaced it and board was much closer, playing with wider horizontal red lines across most of the screen (except top and bottom). Research of other repairs pointed to 2125 rams at 2A to 2D, piggybacked 2D and the problem cleared up. Installed new socket and 2125 ram at 2D to fix the problem.
Game Booted, but Everything was Super Fast, Not Working 100% (3/24/17) – Board looked fairly close to working, it booted up, but attract mode was moving really fast, game didn’t really play when you started, but it was close. Maze was being redrawn very slowly during game mode. Checked roms and with 2114 with Fluke 9010a just to be sure (didn’t think they were the problem) and they were fine. Used Two Bit Diagnostic tool and the board didn’t pass the Interrupt test. Swapped at 74LS74 at 8C as it was already socketed and it fixed the problem.
Slight Hum Bar, Doesn’t work with Jamma Adapter (3/22/17) – Kind of an odd one, board had a very minor vertical hum bar. Also, would not boot on a Jamma test rig (DC voltage was at 2.3 VDC), only on a original AC harness. Replaced big filter caps, D6, D7 and D8, voltage regulator and a few other electrolytic caps, but no change. Turned out Q6 on the heat sink was bad, replaced with a TIP31C and it booted perfectly on both test benches.
Sounds Missing/Scratchy (3/22/17) – Most sounds were missing or barely audible. Bad prom at 3M.
When converted Pac-man to Ms. Pac-Man (11/24/14): The game comes up and plays fine, but then ghosts start flashing diagonally on the screen. It is not all of time and only when the maze screen is on. After it runs for a little while the ghosts start going through the maze blocks (not the on normal maze path). None of this happens when the board is left as Pac-Man. – Slow 2532 roms at row 5, use 45ns or faster.
Gobbling sounds and dying sounds off (11/18/14) – Bad prom at 3M.
Board would constantly try to boot (1/23/12) – Looked like the game was booting up, but it would never quite get there. Reset line was going from high to low corresponding to the resetting at booting. Started pressing on a few sockets and it seem to get further on booting, so I replaced a Z-80 daughterboard socket and rom socket, but no real change. Finally noticed that if I left the game on for a couple of minutes it would get closer to booting and sometimes boot up fully and work. Tested voltage on the two large caps and it was 7.0 VDC. I replaced these caps and it the board booted fine.
Lesson learned: always test power supply voltage first.
Board comes up with “1” on top left corner of screen (3/19/12) - This board was okay, then started acting up. I replaced a rom socket I thought was bad as well as the Z-80 and Z-80 daughter board sockets, but no luck. Started pressing on the ribbon cable and the board would boot. Went through about 3 ribbon cables until I found a good one.
Lesson Learned: always check the ribbon cables.
Most Sounds Missing (3/19/12) – Most sounds were missing and those that did play seemed off. Replaced 1N and socket at 1M as they looked pretty bad (rust). Could see sound signals going to 2M but not coming out, so I replaced 2M to no avail. Noticed that 3M looked pretty rough and when I pulled it legs fell off of it. Installed a new socket, but no change. Checked signals going to 3M and were missing signals and pins 2 and 3, checked for continuity at 3P and 3N and didn’t get any. Ran two jumpers and the sounds came back.
Sounds Off Slightly (3/19/12) - Everything played, just seemed a little off. Replaced most caps in audio circuit to no avail. Reseated 1M and they came back.
Board had zeros all over the screen (3/19/12) – This board was working, but just came up with zeros. Self test didn’t show a ram error, but the troubleshooting guides suggested 4K was bad. Replaced 4K and it fixed the problem.
Boots to “1s” on the screen (3/19/12) – Self test didn’t change anything. Reset and clock lines looked okay, checked the bus with the 9010a and found data lines 2 and 7 stuck together. Found a small socket tail shorting out the two data lines and fixed that problem. Checked the program roms with the 9010a and found that 6E was bad. Board would now come up with an illegible ram error. Tried the 9010a and it said ram 4K or 4N was bad. Replaced 4K and the game now came up with graphics were off. Pulled graphic roms 5E and 5F and they were both bad. Burned new roms and the game works.
Game Plays but characters at bottom of the maze and only move horizontally (3/20/12) – actually a continuation of the last repair, I didn’t notice this until the next day. Game plays fine, but characters were offset low and moved only left and right. Game seemed fine otherwise, started poking around in the final video output section and found that 1E pin 9 input was stuck high. Traced this back to 4C and found that pin 5 was stuck low. Replaced 4C (74LS00) and the problem was fixed.
Garbage on Screen (3/20/12) – Board was recently repaired as Pac-Man Plus but had Ms. Pac-Man roms and Proms installed. Suspected something with the roms as I knew it was recently working. Connected 9010a and tested the roms and found 6E was reporting as bad. Pulled 6E and it verified okay with burner, but tried another rom just in case. Problem was fixed, apparently the original 6E rom had some issue but still verified okay with my burner.
Nothing on Screen (3/20/12) – Board was noted as worked when complete. Installed new roms and it booted with nothing on screen. Connected 9010a and tested the roms and found 6E was reporting as bad. Installed another rom at 6E and the board booted but with horiztonal lines through characters across entire screen. Pushed on graphic roms at 5E and 5F and problem corrected itself so I installed new sockets.
Board would not come up after the new sockets were installed. After a few minutes I found the issue, when replacing the sockets a blob of solder fell out of the desoldering iron. I was able to clean it all up but broke a trace near 4E in the process. Repaired the trace and the board booted fine.
Nothing on Screen (5/16/12) – Tested for voltage and it wasn’t there and I smelled something burning. Starting rebuilding the power supply for the heck of it and finally realized that two large diodes were worked on before and installed backwards. Replaced these and got my +5VDC back. Boardset would then come with a out of sync screen, but coin up and play. Sometimes the game would lock-in and play fine. Started poking around and tapping on chips and found 3R (74LS161) was the problem. It was replaced at one point and the socket and chip legs looked beat, so I replaced the socket and IC and the board worked.
White screen (5/17/12) –Board came up with a white screen, clock, reset, program roms and ram checked out okay. Followed guide in troubleshooting manual and did not see any address signals at pins 5 and 6 at 4A. Traced this back to 5A and noticed the IC was rusty. Found about another 10 rusty ICs that I replaced until the board came up. White screen was caused by bad IC at 3B (74LS157).
White background, red maze, blocks behind characters (5/17/12) – part of the rusty chip repair, bad IC at 5C.
No Sound (5/18/12) – Lost all sounds in testing. Quick look found that 1L was rusty, so I just replaced that at the sound game back.
Two distorted characters on top right and one "zero” on top left (5/29/12) – Continuation of rusty chip repair. This corresponds to a Ram 4M error, so I replaced that but not change. Also replaced the socket, no change. Sometimes board would boot and play fine. Finally realize Z-80 controller had about four more rusty ICs.
Pac-Man color off and some ghosts off (5/29/12) – broken trace at pin 15 of 2A.
Random Garbage on Screen (5/30/12) – Ms. Pac-Man board that booted with just some random characters and garbage graphics. Starting swapping daughterboards and the Z-80 controller daughterboard was bad, had a number of rusty ICs.
Horizontal lines in characters (5/30/12) – Character rom at 5F had a bad socket.