Asteroids Troubleshooting

orion3311

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Hoping maybe someone can point me in a good direction here...this is my first Asteroids board I'm messing with. It's Ray's (Mundomans) and I figured I'd try to fix it now that I have the Fluke and all.

The problem is that it watchdogs in both test and game modes. If you disable the watch dog the test mode pattern looks fine, but its missing the dip switch codes and whatever else is supposed to be there. The crosshatch and gradient are there. In game mode its hard to tell on the oscope but in the cab I think it started to draw a P like for Push Start or something.

I tested Rams and Roms with the fluke, all test good. I also tested the addressing/data for the dip switches - seems to read them perfectly fine.

Can someone point me in a direction from here? These things have a helluva lot of signals going on!
 
Sounds like there is a counter thats not running.. Look for whats triggering the watchdog circuit..It wants to see a periodic heartbeat.
Good luck!

Andrew
 
I started to chase it back...where was a missing line on the counter that does the watchdogging but it pulses when its not in WD disable mode.

I believe I tried to unsolder the DMAGO line and it still watchdogged, which means is something in the MPU, program counter or state machine circuits. The test pattern looks fine so I think the dacs and vector roms are good.

I never realized how involved these suckers are!

Other than what's on Flippers.com, does anyone have any really good Fluke info or scripts as far as testing deeper into this board?
 
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