Galaga Repair Logs

Archived from an old cache page from a GeoCities page…

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11/25/00 Gallag with a ROM 11 error and loss of starfield
This sounded like an easy one except which ROM is ROM 11? In Galaga (Midway) it is 3J. I found out by simply swapping ROMs for known good ROMs from my board it was ROM G7. In messing with the ROMs I have matched up some others. They are G1=3N, G2=3M, G3=3L G4=3K, and G5=3J. I am not sure of the others. The other problem was that the starfield would first simply be a snowstorm then they would disappear altogether. This problem was due to low +5V going to the video PCB. Adding jumper wires to the video PCB from the main PCB fixed this problem (+5V and GND).

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8/17/00 Galaga that would intermittently reset
This Galaga actually had two problems, the intermittent resets and bad/garbaged video. The reset problem got worse as the board warmed up, but the video failures got better, go figure. I first tackled the reset problem since after awhile the game would not come up at all. I first looked at the *reset lines at the Z80 CPUs after the game would no longer come up and found that reset was held low. I then traced the signal back to the reset switch, POR circuit, and the final output to the Z80s. When the board was cold, the reset line was high, sort of, with a lot of noise riding on it. I looked at IC 6B (74LS128)and check for any odd signals. Well I only found that the chip didn’t seem to behave as I expected, touching the output pin 13 reset the game. I then was about to replace this chip and noticed that pins 8 & 9 were shorted to pin 13 by a solder blob to a trace. This basically eliminated the chip from the circuit (tying the input to the output). Removing the short fixed the reset problem. Galaga boards have a very poor solder job and I couldn’t believe this game worked for years like this, but it did.

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8/17/00 Galage repair part II, bad graphics
Now that I had a stable CPU PCB, it was time to tackle the video problem. You could see the game play and sprites fine, but it was like looking through vertical mini-blinds, vertical white lines running through the entire display. After the game warmed up, the lines would go away. So I proceeded to freeze spray the video RAM then the support chips. As soon as I hit IC 5B (74LS298), the problem came back. I then took my finger and warmed the chip up and the failure came back. Replacing this chip fixed the problem.

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3/8/00 Galaga with odd colors and RAM errors
I first replaced the 2114 RAM ICs that the diagnostics were pointing to (there were three bad chips!). The second problem was the colors were off and dull looking. The first thing I did was borrow a known good color PROM at location 1C, this did not fix it, which I was glad since I have no extras. Using the scope, I found a floating high signal on pin 9 of the PROM. I traced the signal to pin 12 of ICs 5A and 6A (74LS365) and found a healthy data signal there. Looking at the board, I found an open trace and jumped it. Now the colors looked great.

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1/10/00 Galaga that would not start, garbage only
I could not get this board to self test at all, it would just come up with garbage. I hit reset a bunch of times and saw for a second “BAD” and something/garbage. So it was trying to give me a message. I then replaced the 2114s and got slightly different garbage. I then replaced IC 1K, a 2016 RAM IC. The game came up, sort of, it went farther before crashing/locking up. I then checked the +5V and found it was at +4.60 on the video board. A lot was being lost along the 50 pin cable, so I soldered wires between cap 1C on the video board and 7N on the CPU for +5V and GND. This fully repaired the board. I then checked the 2114s that I pulled before and found one bad chip.

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8/16/99 Repairing a Midway Galaga, sound problems
This board had the boom sound only, no other sounds. I first swapped the custom ICs but this didn’t fix it. I then scoped out some signals and found there was no output from the 7489 RAM ICs. These chips are getting rare so I had to scrounge them from a dead Pacman PCB.

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7/8/99 Repairing a Midway Galaga, garbage on screen
This board would only come up with stray garbage (not the diagnostics garbage) and nothing else. I tried replacing the Z80 and the ROMs (quick swap) but there was no change. I then scoped around and found that the ROMs were not being accessed at all. There was no chip select to any of them. I traced that back to a 74LS139 (IC 4P) and found it had no output, just signals on it’s inputs. Replacing this got the game booting, sort of. It would go into the demo of the game and the bugs would start flying around in tight little circles instead of large looping attacks as you would see normally. Replacing ROM IC 3N fixed this problem, but I now had another strange problem. Whenever the ship captures your fighter in its tractor beam, the fighter would be sucked up far to the left of the ship instead of below the ship! Replacing ROM IC 3J corrected this odd gameplay. I found a third odd ROM IC 3J During the demo, where the fighter normally gets captured, it would shoot the ship as it was transporting you up for 400 points instead! Any ideas as to how many variants of speedup ROM 3J there are?

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7/8/99 Repairing a Midway Galaga, rebooting
This game would go through the diagnostics, say RAM, ROM, etc. is ok and then promptly reboot and go through the diagnostics again. I could duplicate this on a working Galaga board by pulling either IC 2L (6XX) or IC 4? (5XXX). I swapped both ICs but this did not fix it. Using the scope I found that pin 20 and pin 23 of IC 2L was stuck high (these are data lines). I traced to the signal back to the source and it was there. I then replaced the socket and this fixed the board.

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6/15/99 Repairing a Namco Galaga (bootleg)
This board gave a ROM error. I replaced the ROMs G1, G2, and G3 and found that the “bootleg” ROMs from the internet would not work properly on this board. The game would come up to show the stars and “20000” for high score and lock up at this point. I had another PCB so I copied these ROMs. This fixed the board. The ROMs I had problems with had checksums of 99F7 and 6916, this is the ROM at location 4B (G1), the working ROM has E000. The 99F7 ROM would show the Galaga demo scores and sprites and then lock up. The 6916 ROM would show stars and the “20000” high score only.

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6/15/99 Repairing a Midway Galaga
This board would give a RAM 2H error. Replacing RAM 3F (2114) did not fix this one. I poked around with the scope but did not find any problems. I then replaced the socket for RAM 3F and this fixed the game.

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6/15/99 Repairing a Midway Galaga
This board would give a RAM 2H error. I replaced RAM 3F (2114) and now got a RAM 4H error. Replacing RAM 3J (2114) Fixed the board.

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If anybody has any other tidbits to add, Email me and I will add them here.