Had some good timing on this one.  I while back an operator I do some work for now and then was planning on sending some Galaga boards, so I built up a bench harness. They never showed. My Galaga decided to stop working and I had picked a couple of boards sets up just to have. But I never really worked on any of them. Fast forward and one came in for repair.

Board #1 – In for repair

The board itself is in nice shape and the sockets are single wipe, but not the really bad Scan Bee sockets. On the right are all the Namco custom chips that are heavily tarnished. I swish them around in Tarn-X to get that off and then clean the legs as usual. 

Once I got it all together, the board would not boot. Not surprising. One thing I do with boards with lots of customs is test them one at a time in known working boards. In this case I did not have a working Galaga. I could have tested in another board, but didn’t at this point.

I set up the CATBOX and did some testing, had not done it before on Galaga. Turns out the architecture has similarities to DigDug. All 3 CPUs share the same RAM address space, so all RAM tested clean from all 3 positions. The program ROM for CPU#1 was good. I’ll have to make configs for CPU#2 and #3. 

Put it all back again, watchdogging.. Now I started the part swap Tetris and moved parts back and forth from my board to this one. Finally I got the PCB to boot. GREAT! Last item was No explosion sound – which is controlled by custom 54xx. I swapped a few of those around and the explosion showed up. Then I put the original back and the explosion stayed. 

Moral of the story – the tarnished chips may need to be inserted/pulled a number of times to clear any small tarnish in the socket. They are pretty decent and not worth replacing.. 

The other factor was I determined two of the Z80’s were legitimately bad.

Testing on the bench – everything worked great. Put it in the cabinet and…

This board sounded great on the bench, but in the cabinet it had a very loud bong sound. Capacitor C21 in the audio amp section tested very different from my reference board. Replaced it to fix the problem. Bench power and the game power was obviously just different enough.

After about 20 hours of run time, one of the 08xx customs died causing the game to crash. Replaced.

Board works!

Board #2 – One of my extra Galaga PCBs

This one turned out to be easy. Same tarnish issue as above. Cleaned all the chips, Deox-it.

Booted but the star field was messed up. Reseated the 05xx custom.

Board works!