Galaxian (Bootleg) Repair Logs

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Repairer: Arcade King
Forum Thread: Galaxian PCB Repair

Swapped this board for a Juno First. This thing was in bad shape board itself was fine but a lot of corroded chips.

Galaxian bootleg before repair.jpg

  • Bad 74ls138 @ 8M,P,N
  • Bad 74ls194 @ @L,K,L,H
  • Bad Prom@6L
  • Bad 74ls74 @ 6C, 5C, 6F
  • Replaced heavily corroded 368 and 107 at 1E and 1D
  • Other corroded chips: 5D,6N,3M,3R I'm sure theres others but cant remember replaced so many.

Up until now I've been able to get nothing on the screen except the occasional starfield and sometimes it even boots and plays. All you see is starfield and you can see where ship is shooting but nothing else.

I now have some garbage on the screen in the form of letters numbers etc and sometimes the game will boot and play. The culprit was a 74ls157@3L. Bad 74ls367@9D fixed some of the text in game and sprites.

Found a Bad 74ls157@2F I'm pretty sure this was what caused the double text and sparkles on the screen. Can't be sure because the game is going through Ram/Rom test then saying Bad Rom 3 then resetting. This I take as a good sign because before It was just random garbage and sometimes the game would boot and play. I'm suspecting one of the 74ls367s @ 5L or 5M I've been able to reproduce this on the other board when I was working on it.

I was right well mostly. The chip itself was fine but I found a burnt out trace between 5L pin 15 and ground. Board now fires up and runs. All graphics look great. Looks like the 157@3L was the problem with the graphics.

Galaxian bootleg fixed.jpg

Colours decided to die, bad 74ls161@3A. Special Note: Only SS branded chips would work properly here all other branded chips I tried would not work 100%.

This bootleg uses a rider board with 2 IC's a 74ls74 and 175 and 5 HM2510 rams. This board replaces the 5 27LS00 rams used on the original board. The Bootleg also is missing the 74ls174 that sits just above the 27ls00 rams. These rams are for the diving aliens without it you dont see any diving sprites but the rest of the game is normal.

This board was in bad shape and when I plugged it in the text would all change to one colour. The 2 IC's on this board were corroded badly and I don't have any replacements for the rams if they are faulty. I decided to replace all the IC's and Sockets on the rider. This was a good move all the colours are now correct and you see diving objects. Only problem is they are split in half and the top part of the sprite is at the bottom also, at least they are the correct colour and working. This suggests the rams are ok so i need to look for something faulty on the board itself.

Found the problem a bad 74ls157 @ 3J Diving sprites and now 100% so relieved the rams were ok.

Time to add a amp to this old board and test the sounds. It looks like this board never had a amp put on it and was wired to run a external amp. There was one wire from where the volume pot should have been to where a cap should have been. Spending a while looking at where a amp was supposed to go I finally concluded this board would have used a MB3712 or MB3713. Same chip just pinouts around the other way. These are very common on boards like Pacman, Gallag, Mr Do! etc.

Wiring the Amp up was easy, I just used a scrap bootleg Pacman I had on hand as reference. Need to complete the amp circuit was:

  • 1x2200 uf cap
  • 1X470 uf cap
  • 1x47 uf cap
  • All caps 16 volts upwards
  • 3x104z mylars
  • a Volume pot
  • and naturally the amp

The pinout is slightly different for this amp. A common ground is needed for - sound and on the solder side where negative would normally go is where your positive line is Make sense? To keep the orignal pinout I jumped a wire from common ground to pin 5 parts side.

Fired the game up and the Amp works great! there are some sounds fault though. Only sounds present are the start up tune(if you can call it a tune), alien diving sound and alien explosion.

Missing is the background noise(rack movement), all you hear is a constant hum, the ships firing noise and the ship explosion which is different to the alien one. Missing background rack movement was due to bad LM374 @ 7T Missing explosion and fire was due to bad CD4066(Quad analog switch and mutiplexor) @ 7R Diving sound was badly crackling changing a 470uf cap @ C37 fixed it.

Only other problem I noticed was the background Rack noise was VERY quite. Doing some poking around I tested the resistors around where the rack noise is generated namely the 3 455(normally 555) chips. I found a bad 5.1k resistor @ R34 the resistor was reading 73k! Replaced resistor and all is good. Sound is now 100%

On a final note one thing I noticed about this board ever since I got the graphics working was how bright the display was. Most noticable was the bottom 3 rows of aliens were a bright blue colour. I had a sneaky suspicion it was a group of resistors that sits below the colour prom at 6L. Turns out I was right. 3 of the resistors were the wrong value being 22 ohm instead of 220 ohm replacing these @ R74,R76 and R79 restored the colours back to what they should be....stupid bootleggers. Its a shame in the pics you can't see the difference too well.

Just realised I lost most of my repair and PCB pics after I had to reformat. The Only pic i have of the PCB is one after I just started working on it. Missing is the big rider board with 2716s which holds the program for these bootlegs and I removed the Ram board.

Galaxian bootleg pcb.jpg

I'm going to convert this board to Moon cresta using The Profs Hax


Found a few HM2510 ram equivalents that work.

Intel D2115A - Pacman Bootleg
Intel D2125A - Car Action
Hitachi HM2511 - Crazy Kong

Repair Logs converted to wiki format by Brad from Aussie Arcade.