So I found a dead Gorf on Craigslist. It was an older ad, but was still available when I inquired. Dude I picked it up from had done some pretty impressive restorations on some other games.
Anyway – it was dead alright. Shows a blank screen that looked overly blue due to how the monitor was adjusted, no starfield was visible. Slid the test switch over and power-cycled, but this made no difference either.
The previous owner had mentioned that he had done some work on it. I saw some of his other previous work on other boards of his and while not perfect (some cold joints, or not enough solder in some places leaving “pits”), it was not horrible and definitely no worse than what I was doing when I started out.
Anyhoo, starting with the power PCB – the previous owner said he had already replaced the caps, but I wanted a second look at it, JIC. On the solder side of the board, some larger traces has been lifted off the board during some previous repair work (I do not think it was his, maybe someone before him?).
It looked like the someone used a serious soldering gun to do the work, because there were scorch marks on the board(!) and flux was all over the older work too. Continuity was where it was supposed to be, so I guess that while it was ugly, it worked.
Hit the previous work with a small wire brush to clean up some of the flux, and reflowed solder on it and the connector pins, just to be safe. While I was doing this I noticed that an IC had two pins soldered together, but each pin had its own separate trace, which looked suspect. Verified with the schematics that the pins are NOT supposed to be soldered directly together and fixed it (they are actually supposed to be connected through a fuse).
Powered the game back up and it came up with a rolling screen but I could make out score displays at the top. Also was showing some solid “blocks” that made me nervous and some color distortion. Was able to get the screen to lock with a simple monitor adjustment. Blocks were just the test screen – I had forgotten that I left the test switch closed.
Game was already set to free play, so I started a game. Immediately noticed that some sounds are missing, and no speech. Adjusting volume controls did nothing to fix it, but I quickly determined it was channel 2 that was broken.
Checking voltages at the channel 2 speaker shows it at a constant ~14 volts! Metering the input to the amp board shows sensible readings that change while the game is running, so I think the input is good.
Taking the amp board out and metering the transistors shows some strange readings, but they were in-circuit. Swapped the two audio lines at the connector (pins 4 and 6), and I was able to hear the other set of sounds, but still no speech. After paying closer attention, I noticed that I was getting a a click or two when I was supposed to be hearing speech. So I think I verified that the channel 2 section of the amp is bad and the Votrax SC-01 is bad, too. That last part really IS bad, because they are not easy to find!
Decided to shotgun the entire channel 2 section of the amp board, JIC – this is old hardware, after all.
After doing that I remembered I forgot to actually check the speaker itself. Sure enough, it was supposed to be an 8 ohm speaker, but it was shorted. Replaced the speaker and connected up the repair amp board and now I have all sounds except speech. The mother ship explosion never sounded so good! 🙂
The SC-01 chips are getting hard to find and are a bit pricey. But I do want the game working fully again, so it might be worth it.
Update: Purchased an SC-01 from GameRoomRepair. Installed and Gorf has its voice once more!