Galaxian

Galaxian Board Repair 

Galaxian was one of the first boards I started working on way back when as I had a lot of them, repairs are well documented and it has two helpful troubleshooting manuals. It was also one of first games I ever owned way back when.  A few tips below and a bunch of repairs follow.

Repair Procedure

  1. See Galaxian Troubleshooting Manual.
  2. Always use a known working daughter board with new roms.
  3. Always replace character roms at 1H and 1K with new EPROMs (mask roms are so brittle).
  4. Check for clock signals at Z-80 and other test point (per manual).
  5. Check for reset high signal. If bad check H and V signals and 74LS161s

Repair Log

Dead, Power Issue (10/12/13)

  1. Fairly clean board, replaced 10,000 uf caps, voltage tests at 2.4 volts or something. 
  2. Replaced voltage regulator at IR1, now have +5 VDC.
  3. Board boots to “Bad Ram 3” message.
  4. Replaced 9101 / 2101 ram at 5F, no change.
  5. Replaced 9101 / 2101 ram at 4F, board now works!

Garbage on screen, loud buzz (10/11/23)

  1. Very clean board, didn’t do any preventative maintenance.  Clock signal looked good, reset was low.
  2. Probing around found that 32H, 64H, 128H and 256H signals were high or low.  Checked 74ls161 at 4A, had some input, but output stuck high or low.
  3. Used a logic comparator to check all the 74LS161s that drive the H and V signals. When I used it on 4A game would boot.
  4. Replace 74LS161 at 4A and board now works.

Sprite Issue (Diving Invaders and Title Screen Invaders) (10/10/23)

  1. Board had some rusty / cruddy ICs, but not too many.  Replaced sockets for roms at 1K and 1L already and 74LS107 IC at 1D. 
  2. Board boots up and plays, but has sprite issues. Two of the three invaders on the title screen are wrong (garbage graphics).  Diving invaders / sprites have similar graphic issues.
  3. Replaced all four 74LS194s at 2L, 2K, 2J and 2H. All of these are rusty legs and I was sure one of them was the issue based on the troubleshooting manual and their condition.  They weren’t the problem. Board had the same issue.
  4. Research indicates 74LS273 at 4L could be the issue. Start probing around and find outputs at pin 5 and 2 are stuck high. Inputs have activity. Replace 4L to fix the issue.

Double Image on most of screen (10/9/23)

  1. Clean board that was working. Issue developed during bench testing.
  2. Bad 74LS86 at 3B, piggybacking it corrected the issue. Used troubleshooting manual to determine the bad chip. Easy fix!

Missing Invaders, Horizontal Line above score (9/4/20) – Board was repaired and sold, tested it prior to shipping. Assumed a 27LS00 ram was bad, started probing around and found LBA2 at pin 15 was low on all pins. Traced back to 3T, still low, at 4T, pin 12 it was low.  4T was socketed, swapped it out, but no changed, removed and check socket, it was installed cleanly.  After socketed removed 4T pin 12 was still shorted to ground. Inspected traces and found a small cap lead on the back was bent over causing 4T pin 12 to short to ground. Cut the lead, installed new socket at 4T and board works again.

Bad Ram 1 (2/7/18) – Clean board, booted to Bad Ram 1 message. Removed and replaced 2114 at 7N to fix the problem.

Ram 1 Error (3/30/17) – This was something on the satellite board as I burned a new set of roms and this error popped up.  Used Fluke and most roms tested bad, swapped roms into a working satellite board, Rom Z was bad.

Dead, Nothing on Screen (3/30/17) – Voltage was testing at 2.5 VDC. Replaced filter caps and the transistor at IR2 (TIP31) and the voltage came back, board came right up.

No Sound (3/30/17) – No amp buzz, checked LM324 at 7T and sounds seemed to be generating. Replaced main amp LM1877 and sounds came back.

Scrolling stars only (5/4/16) – seemed to kind of boot through initial self test and then went to scrolling stars on the screen and that was it.  This was after I installed a new set of program and video roms.

Rom Error (5/4/16) – Board booted with rom error, burned a new set of program roms and it booted up, but with color issues.  Suspected video roms, burned a new set and the problem went away.

Nothing on Boot (9/15/15) – Board was sold working and came back to the shop with nothing, clock signal was not at CPU but appeared to be okay from crystal. Replaced 1E and 1D as I thought it dropped out here, but no change.  It was missing from 5A and 6A, pin 2 as well and eventually tracked it down to 7474 IC at 6C. Replacing this fixed the problem and board came back to life.

Bad Ram 2 (3/19/15)

  1. Before doing anything I replaced the 10,000 uf axial power supply caps, cleaned edge connector and burned a fresh set of program roms for the daughterboard as the proms looked rough.
  2. Board reported a bad Ram 2 on boot. Replaced 2114 at 3F to fix this issue (reported bit Address Error 40).
  3. Board now played with no sound a video issue with text in test mode (had some lines in it).
  4. Replaced video rom at 1H to fix this issue.
  5. No sound was due to bad LM1877 amp, there was not static or noise prior to replacing it.
  6. Most sounds came back, but fire and ship explosion sound (when you died) were missing.
  7. Replaced 4066 at 7R to fix this issue.

Dead, nothing on screen (11/18/11) – Checked for clock signal on 1E, pin 1 per manual, no clock. No clock on CPU.  Replaced 18.432 mhz crystal and the game came up perfectly.  Easy fix!

Dead, nothing on screen (11/18/11) – Voltage was low, 2.4 volts.  Replaced diodes D4 and D5, no change.  Replaced voltage regulator and voltage was back at 5.0 VDC.   Got horizontal lines on the screen (wide bands).

Started poking around on ram chips 1N to 1T – a few of them had low inputs that should have been pulsing. Traced back through  2R, 3P, 6P, 6R.  6R was getting a proper wave signal on pin 9.  Traced this to 4D (74LS139). This chip was replaced at one point, installed a new socket and replaced it. Pretty much the same thing, although I got an occasional bad ram message on the right edge of the screen.Piggybacked Ram 4F to read the message.Bad Ram 1.Replaced 2114 chips at 7p and 7N.

Still got lines on the screen, but it was resetting like it was reporting a bad ram message.  Went back to 6R, still no wave signal.Traced back to 4D and then 5C.  Input wave signals on 5C looked good, but outputs were dead. Replaced 5C and wave signal was proper.  Still get lines on screen, but now I got bad Ram 3 message in test mode.

Replaced both 2101 Ram chips per ram message. Game comes up and is playable, but a ton of horizontal lines across the screen.  Double checked character rams, both were okay.  Starting poking around 2K, 2L as they are after the character rams.  Output on 2L, pin 12 (QD) was stuck low.  Replaced 2L and many of the lines went away, but a few still remain. Rechecked character roms and they were okay.  Starting replacing other 74194s as I couldn’t figure out which (if any were bad).  After replacing 2K, 2L and 2J as well as 3L the picture came back.  

Garbage on screen (11/22/11)– Random garbage on board, sometimes it was different. Tried test mode, sometimes I’d get Ram Error 3, sometimes the garbage.  Ram 3 4F was socketed, starting pushing it on at the ram error would change color.  Changed the socket on this ram chip and I no longer got any ram errors, just a consistent garbage screen.  

Checked the clock signals, they were okay, checked for high reset, but it was low. Started tracing back the reset line and found that 6T and 6S were not getting a signal at pins 1 VBLANK as they should be. These chips drive the reset line.  Traced the VBLANK signal back to 5C, pin 5 where it looked just fine.  Figured there was a broken trace as it wasn’t making to 6T and 6S.  Found a broken trace on the back of the board. Reconnected the trace and the board fired up in play mode but without sound and the invaders were missing colors in attract mode.

Manual points to 27LS00 rams at 1N to 1T.  Found that 1P was bad, replaced and the colors came back on invaders but colors were missing on diving invaders during gameplay. Rams all checked out okay, noticed some corrosion in corner of board and after pressing on 1T the colors would come back. Replaced the socket at 1T and the invaders looked good.

Still no sound, amp was clearly replaced and I noticed it was a LM339, which I do not believe is the proper amp chip. In any case, there was no audio hum at all so I replaced the amp with a LM1877 and I had sound again.  Problem was it would cut down to a lower sound after a minute or so of game play.  Starting replacing bigger caps and some resistors as well as pot in the sound circuit with no change.  Checked manual and it recommended the .1 uf caps at C46 and C47.  Replaced those and the problem was fixed!

Lessons learned: Always check board for damage first.  Also don’t assume sound problems are the big caps or pot. Turned out the smallest caps were the cause.  Always pressure check socketed chips to look for bad sockets.

No Video (11/22/11) – Nothing on power-up, power tested good.  Clock signal on CPU and at crystal looked good. Board had a note that there was not signal at 6M pin 11.  This was a CLOCK signal. Sure enough I checked and there was no signal.  Started poking around and traced back to origin 1E, pin 4 (manual is incorrect here) and the signal looked off. Swapped in another IC at 1E, but no change, which puzzled me as the input side looked good.

Was really stumped here, started poking around more, address lines looked good, couldn’t really find any issue.  Went back to this CLOCK signal and after a long while realize that the line was shorted to +5VDC. There were already two ICs replaced on this line, so I rechecked their sockets to no avail.  Finally started cutting the traces for the CLOCK and narrowed it down to one stretch on the boardset, but not an IC. After some scrapping I found a real small piece of metal shorting the line. Cleaned off the trace and redid my cut traces and the clock signal came right back. Game comes up with horizontal lines though….

Horizontal lines like this are usually the character roms (1-J, 1-H) or one of the four 74194s after those roms.  Those were already replaced and known good, I started probing the 74194s. Clock signal looked normal, starting looking at data lines with scope.  Pin 3 on 2H was low, no signal, checked for signal at 1J, pin 13 and it was as it should be. Check continuity from pin 13 to pin 3 on 2H and it wasn’t there.  Replaced rom socket at 1J and the lines went away. Game plays, but invaders are missing one diving…..

Missing diving invaders  and invaders in attract mode (or missing colors in invaders) are usually the 27LS00 Ram chips. Replaced 1N as it seemed to correspond with the issue, but not changed. These rams were soldered, so I started probing around, found that address line 1N, pin 11 was dead. Replaced ram at 1N and some of the invaders colors came back.  Kept replacing rams until the problem was resolved, but now I get “sparkly” invaders….

Flashing B&W stuff on Screen / Bad Ram BError (11/23/11)–Clean board, put it in test mode and I get “Ram Error B”. Go to manual and of course there is no Ram Error B, only 1,2,3.  Recheck daughterboard and look at the address lines, they are not moving.  The two 2101 rams were socketed and okay.  Of course the 2114 ram were soldered in, I started with 7N and 7P, removed and installed new socketed rams, but no change. Moved on to 2114 ram at 3F and that fixed the problem. Game comes and plays just fine.

Bad Ram 2 Error (11/23/11) – Board in test mode and I get “Bad Ram 2” error message, sometimes with some dots across the screen.  Replaced both 2114 rams at 3F and 3H and there is no change.  Pulled out the 9010a and performed a short ram test on all rams. Both 3F and 3H locations report bad as well as 7N and 7P.  I replace 7N and 7P and those rams now report OK using the 9010a, but I’m still getting a Bad Ram 2 message.

Bad Ram 2 Error (11/24/11) – Board in test mode and I get “Bad Ram 2” error message (no dots on screen).  Replaced both 2114 rams at 3F and 3H and there is no change.  Check pin 2 at 5J and there is no signal. Replaced 5J and the problem was fixed.

Bad Ram 2 Error (11/28/11) – Board in test mode and I get “Bad Ram 2” error message (no dots on screen).  Replaced both 2114 rams at 3F and 3H and there is no change.  Check pin 2 at 5J and there is no signal. Replaced 5J and the problem was fixed. Second time I have had this issue.

Nothing on screen (9/25/12) –Nothing on screen, checked clock signal and it was missing. 74LS368 at 1A was installed backwards.  Replaced that to get a clock signal, but still nothing except for buzzing.  Reset signal was low, traced this back to 74LS161 IC at 3A with dead outputs.  Game now boots up and plays but has horizontal lines across the screen.  Both graphics roms at 1H and 1K were rough (legs fell off after removing them). Burned new roms and replaced sockets at 1H and 1K as well to fix the problem.

Finally, during game play a couple invaders were at the bottom or top of the screen. Also did this in attract mode. Traced this to the outputon 74LS32, pin 11 at 3S which was stuck high.Replaced 74LS32 to finish the repair.

Game Plays, but Graphic Issues (9/25/12) – Game plays but sprites were distorted, different characters, etc.  Roms at 1-J and 1-K were new, but socket at 1-K looked dirty. Replaced socket at 1-K to fix the problem.  During testing I noticed the diving invaders were missing some colors which usually means one of the 27LS00 rams at 1N to 1T is bad.  Of course they weren’t socketed (they sometimes are on Galaxians).  Starting probing around and found pin 6 at 1P to be dead (other rams were pulsing at pin 6).  Replaced 1P to fix the problem.

Board worked then developed horizontal lines on screen. (9/26/12)  Bad socket at 1K (again).  Almost to the point where 1K and 1H should just be replaced as well as the sockets on these boards.

Board booted to garbage. (9/26/12)  Reset line was high (which is normal), clock signal was good, program roms and CPU were good.  Started probing around the roms at 4F and 5H (there were good) and burnt my hand on at 5J. 

Replaced 74LS245 at 5J and got different garbage on screen. Put the game in test mode and it looked like it was trying to display a bad ram message (only saw a few characters on the screen, where it normally displays bad ram messages). A couple signals on 3F and 3H rams looked off so I replaced these two 2114 rams to fix the problem.

Board booted to streaking lines (10/1/12) – Started by checking the crystal and when I touched the crystal with probe it screen would change. Clock signal didn’t look right.  Replaced crystal and game booted to Bad Ram 1. Replaced 2114 ram at 7N and board now booted to Bad Ram 2. Replaced 2114 ram at 3F and the board booted and played fine.