Asteroid PCB Repair Log- 1st time PCB work

jjvaughn83

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I have a 1979 Asteroids upright original, unsure of the version of the PCB. The PCB has been repaired in the past (has asteroids written at the edge connector in sharpie, like it was in a pile of others).

Symptoms:
-Game play seems to be fine. Start buttons blink, audio is working.
-Game will start but no ship is shown. Just a white hot dot. Bullets can be seen and all controls seem operational.
-About 50% of the asteroids show correctly. When they don't show, they are a white dot like the ship. Once visible larger asteroids are shot and they break up, they always turn into dots.
- UFO can not be seen but audio let's me know it is on the screen.
-It will play all day, keep score, take your hi-score, etc. etc. Only issues are with the video.
-I've played with brightness, contrast, x/y pots. Some improvement but still missing ships, partial asteroids and UFO.
- 4.8V (+/- 0.1) is found all over the PCB in multiple areas.

Test Mode: No cross hatch on screen. DIP settings show in the center and fuzzy white dots (1/4" dia) in corners (lower left, upper right)

Test Mode Audio (3 medium tones then 1 low tone) is identifying RAM "R4" failed self test.

Changed the Vector generator Rom at N/P3 with a new one from Steph. (I fried the old one reversing polarity after cleaning)

Next step: Ordered new 2114 chips (and sockets) from Jameco to replace all 4 of the vector generator RAMs (R4, P4, M4, N4). Also coming is a logic probe so I can really get into troubleshooting this board.

Question: Is there supposed to be audio in the Attract mode of this cabinet? Mine is dead silent.
 
Don't replace anything on an Asteroids board that is not already socketed unless you know it is bad. Especially if you don't have excellent skills. Traces will lift just by seeing the iron coming toward them. You could break a connection between the top side and bottom side w/o even knowing it.

Use the built in diagnostics. If that 2114 is program ram, the game is running, chances are that RAM is OK.

Your problem sounds like it is likely somewhere in the DVG, and you are going to need a minimum of a logic probe to get any further with it.

I've repaired Asteroids boards with trace damage (for a fellow KLOVer). It was tedious, but I fixed it up real neat and brought it all back. The damage was discovered when repairing the board.

After a bit you learn which boards are 'tough' and which are 'wimpy'. Sega G-80 boards are pretty robust, Atari Asteroids love to lift traces (as do Space Duel's, and many other Atari boards of that era).

If you insist on changing something out before verifying it is bad, use flush cutters and cut the leads of the ICs you are removing off close to the chip body, use needle nose pliers and a soldering iron to remove each leg individually. Then carefully remove the solder from the through holes.

Swapping chips if you are no sure they are bad is wasteful. Sure, some of these chips are plenty now..... but someday they may not be. Even through hole TTL is at the point of going away. Every year brings more and more chips no longer made new, and when the easy to get stock is gone, prices are going to skyrocket with eBay sellers selling chips of unknown quality and origin at premium prices.

IIRC correctly, Asteroids has chips in the DVG responsible for 'scaling'. I'd get a logic probe and start there looking for stuff stuck high or low. Once you identify a suspect, if you have one, do the same test on a good board to compare, as sometimes leads on a chip don't change state often, or can be tied low or high (the latter ones being easily determined by looking at the schematics).

Good luck with your repair.

Good luck with your repair.
 
cwilbar: Thanks for your response. I will be leaving the soldering iron down for a while and use some of your points for checking this board out now.

The 2114 that the test-mode says is failing is 1 of 4 Vector Generator Ram which keeps me pointed in that direction.

Reading through the schematics, I found mention of Scaling in the Z output which receives its signal from the vector generator state machine. The logic probe should be here this afternoon and then I will be teaching myself how to check these boards out. Thanks for all the help!

 
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