Astro Invaders Arcade Restoration

A friend gave me a few arcade games. One of them is Astro Invaders.  I was told that the machine used to work sporadically, sometimes requiring a whack to the side to get it to work.  Now it just has these red and black vertical bars and repeats this incredibly annoying "pew, pew, pew..." sound over and over.  When I pound the side of the cabinet, the screen flashes and there is an explosion sound.  Then it goes back to the red and black screen.  I was going to sell it as-is, but I decided to restore it instead.  If I decide to sell it later, I can probably double my money if the game works.  I've never worked on an arcade before so this will be a good learning experience.

screen problems

Luckily the game included all of the manuals and schematics.  I read over that material to see if it said anything about this red screen.  No luck.  So I opened up the back of the cabinet and identified all of the sections of the game.  I noticed that the power supply board was hanging loose in the cabinet.  I grabbed four 6-32 screws and secured the power supply board to its mounts.

power supply board

Next came some step-by-step troubleshooting.  I started with the power supply as that is the first section of the game.  First I checked the fuses.  I used my multimeter to check for continuity.  All of the fuses were good.  However, I did notice that one of the fuses was loose in the mount.  I removed the fuse, pinched the mount together, and reinstalled the fuse.  The game still didn't work, but now when I whack the side of the cabinet nothing happens.  Looks like the loose board and/or fuse was causing things to short out.

To see if the power supply was working, I checked the voltage test points (labeled "TP") on the circuit board.  The manual and the board tell you what voltages to expect at the test points.  I checked TP1.  It should be between 5.3 and 5.6 volts.  It measured less than 2 volts.  So I adjusted the small potentiometer next to the test point until my meter read 5.3 volts.  Suddenly the repeating noise stopped.  I peaked around the front of the cabinet and behold!  The game was working.  I played for one life.  But when my ship was destroyed, the game crashed and went to a blue screen.  So I checked the other test points.  The 12 and 15 volt test points were way off (< 3 volts).

A few hours later I powered up again and checked the voltage directly at the voltage regulators.  The voltages were all as expected, about 11.8v from the 7812 and 14.9v from the 7815.  I checked the test points again and they were all within spec.  I played the game and everything worked perfectly.  Hmmm? As happy as I was that it worked, I need to know why it wasn't working before.  Otherwise, it might happen again.  And it did.  Every once in a while I would get the same screen problem.  Eventually, I traced the problem to a loose wire connector on the power supply board that came from the SG323 regulator (upper left corner of the power supply in the above picture).  I twisted the connector around until it worked again but it will need to be replaced when I get deeper into the restoration.

It's alive!

Well that was a bit frustrating but relatively easy.  Next, I'll fix the lights and locks.  Stay tuned.