*** Note: I format these in a browser - not sure how they will come up on a phone. They are cross posted from my site
***
This is one of mine..

This is the 'after' shot. Arcade customer sent in a MC board for repair (next one below) but wanted a spare since Missile Command is now down at their arcade. I had one that I'd picked up a while back and got it running while it is in transit. This particular board had a lot of little things wrong with it.. One thing I do like is the RAM are all ceramic packages. It had no RAM or ROM errors. It's not the brightest and shiniest board I've ever seen. I did wash it.
Items of note:
Probing the watchdog circuit - the watchdog was not being cleared.. Working backwards..


/WDOG was stuck high going into LS00@D8. It is generated by 7442@E8 Pin5. Replacing it fixed the watchdog circuit.
The colors were off. I determined that it was the BLUE and tested the R/G/B outputs at the video connector with the scope. Working backwards I found the following:

Something that is pretty rare (at least for me).. R46 had drifted WAY out of spec. I could see good 'BLUE' signal going in and really bad signal coming out as compared to RED and GREEN resistors Testing the resistor, it read 2.8K ohms.. not 22 ohms. It was the original - maybe a monitor issue zapped it? Replaced it and colors restored!
The last item was color trails being left by the crosshairs...
This one I did a quick search and found a repair log Game board #16 and it looked nearly identical. One thing about this is it only started after the board warmed a couple of minutes - thermal failure. I sprayed it and some of the other chips in this area with Freeze Spray but the issue didn't clear.

Repair log said replace the LS153@P7. Before that I did clip onto the chip with a tester and it seemed to effect it. Replacing the LS153 did nothing.. Below that is the LS251@N5. Probing that showed bad outputs on Pin5. I hit this chip with Freeze Spray (a little better than the first pass earlier) and the issue cleared. Replaced it and the color trails were fixed.
Board works!
This is one of mine..

This is the 'after' shot. Arcade customer sent in a MC board for repair (next one below) but wanted a spare since Missile Command is now down at their arcade. I had one that I'd picked up a while back and got it running while it is in transit. This particular board had a lot of little things wrong with it.. One thing I do like is the RAM are all ceramic packages. It had no RAM or ROM errors. It's not the brightest and shiniest board I've ever seen. I did wash it.
Items of note:
- Missing Power LED - replaced
- Missing Q1 (coin counter transistor) - replaced
- Start 2 test point was missing - added it because I have them
- Colors were off
- Board was watchdogging
- Cross hairs were leaving trails
- Crystal was fine, the can was rattling - replaced it
- Edge connector got cleaned up and liquid tinned. Copper was a little exposed
Probing the watchdog circuit - the watchdog was not being cleared.. Working backwards..


/WDOG was stuck high going into LS00@D8. It is generated by 7442@E8 Pin5. Replacing it fixed the watchdog circuit.
The colors were off. I determined that it was the BLUE and tested the R/G/B outputs at the video connector with the scope. Working backwards I found the following:

Something that is pretty rare (at least for me).. R46 had drifted WAY out of spec. I could see good 'BLUE' signal going in and really bad signal coming out as compared to RED and GREEN resistors Testing the resistor, it read 2.8K ohms.. not 22 ohms. It was the original - maybe a monitor issue zapped it? Replaced it and colors restored!
The last item was color trails being left by the crosshairs...
This one I did a quick search and found a repair log Game board #16 and it looked nearly identical. One thing about this is it only started after the board warmed a couple of minutes - thermal failure. I sprayed it and some of the other chips in this area with Freeze Spray but the issue didn't clear.

Repair log said replace the LS153@P7. Before that I did clip onto the chip with a tester and it seemed to effect it. Replacing the LS153 did nothing.. Below that is the LS251@N5. Probing that showed bad outputs on Pin5. I hit this chip with Freeze Spray (a little better than the first pass earlier) and the issue cleared. Replaced it and the color trails were fixed.
Board works!











