I don’t work on video games that often, much less vector games. This Asteroids had two problems on power-up that would resolve themselves after a few minutes, and a graphics problem that didn’t.
The first and easiest problem to fix was the sound. The sound wouldn’t work until about a minute or so into gameplay. I just recapped the power supply so I know it wasn’t a capacitor issue. I swapped in another known good power supply and the sound worked every time. Sometimes troubleshooting is just swapping in a known good part. It’s not sexy, but it gets the job done.
The test power supply hadn’t been capped yet so I decided to fix the original unit. Replacing both TDA2002 amplifiers did the trick. Sound works on startup every time. Remember, on Atari games of that era audio amplification was done on the audio/regulator (A/R) board, also known simply as the power supply.
The second problem wasn’t too bad. Basically, I got lucky. The picture had graphics issues around the high score, the player 1 score, and the text at the top of the screen when putting your initials in for a high score.
Unfortunately, I didn’t get a picture of the distorted text to show you. I was looking over the schematics and I noticed there were a few 74LS161 counters in the vector timer circuit. I’ve seen *LS161’s cause graphics problems before so I thought, what the hell, I’ll swap in some new ones and see what happens.
Here is the datasheet for the 74LS161 if you want to learn more about it, what it does, and how it works.
One thing to note here, the distorted text was consistent. It always happened, and it always happened in the same place. That tells me something like a counter such as the 74LS161 could be the culprit. I saved the old ones and 2 of the 3 tested bad as you can see below. Problem solved.
Don’t try this at home children. I threw a dart and got lucky. I didn’t have any of my testers with me at the time so I had to wing it.
The last problem was the entire picture was scrambled and collapsing when turning the game on after it sat a while, it wasn’t triggering the spot killer though. The spot killer turns off the electron beam if the monitor isn’t getting a deflection signal from the logic board. On vector monitors, the beam will just point to the center of the screen and eventually burn the phosphors off the tube. That’s why you’ll occasionally see a vector game monitor with a spot burned in the center of the screen as is the case on this picture tube.
Raster games don’t have this issue since the beam will always constantly sweep the entire screen, with or without color or sync signals.
If the game was turned off and back on within a few minutes the picture would come back up immediately. I started thinking this was a temperature issue. So I decided to “cool off” the video output section of the board with the blowgun. I edited the clips together of the video I shot into one short video. You can see how the problem progressed, how I duplicated the problem, and the fix.
As you can see in the video when I cool off the board with the blowgun the picture gets distorted and after a minute or so comes back on. After the repair, the cooling of the board doesn’t make the picture go crazy anymore.
I was able to isolate the area to about a two-square-inch section of the board. There are only a few components, resistors, diodes, and capacitors. Resistors tend to go open when they fail so the problem would be the other way around, the picture would start off good, then get scrambled unless the resistor was totally open.
Just to be sure I checked the resistors, all we’re within tolerance. That really leaves only one thing left. The capacitors. I have an ESR meter but that’s for testing electrolytic caps. So I swapped out the two caps right there C88 and C89. They are mica caps and I didn’t have any new ones around so I pulled two off a parts board.
I put the board back in the game, held my breath, and turned it on. It’s FIXED! Just to be sure I cooled the board off with the blowgun a few times and the picture was locked in and solid. Capacitors can often be overlooked when troubleshooting. I can’t tell you how many times I’ve seen a tech change a bunch of chips only for the problem to be a 9 cent cap. Sometime in the not too distant future I’ll tell you about the Centipede with this issue.
I kept the game turned off and checked it several times over the course of a few days. Started up perfect every time. Having a basic understanding of what the parts do, how they work, and more importantly, how they fail, can aid in troubleshooting.
I’ve said it before and I’ll say it again, a part can test good but fail under a load. Sometimes all you need is some experience, intuition, and a little luck.
‘Till next time, Frank