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Space Invaders PS problem
- Thread starter DP Louie
- Start date
All your symptoms so far point to a bad CPU socket I think. If you removed the roms and the lines are corrupted/garbled, thats a bad ram symptom but again can happen if the cpu isn't making good contact or malfunctioning. If random sounds are happening too (with no roms), thats REAALY something wierd going on with the address bus, and again I'd suspect a cpu socket or chip (8080).
If it were me looking at it, I'd first replace the cpu socket, next, double-check the boards over to make sure there's no scratches shorting a trace somewhere. I think after that I'd look at the 174s (I think) on the sound board that trigger the sounds, as they may be feeding noise into the address busses.
(one way you can check the last thing first is to pull the CPU socket, and put a logic probe on each address line to see if any are pulsing while nothing should be happening).
The fuses on the power brick could definitely be an issue too - I've seen fuses go bad where they don't blow, but just break at the ends from age. If you pull a fuse and the end pops off - that could be the issue!
If it were me looking at it, I'd first replace the cpu socket, next, double-check the boards over to make sure there's no scratches shorting a trace somewhere. I think after that I'd look at the 174s (I think) on the sound board that trigger the sounds, as they may be feeding noise into the address busses.
(one way you can check the last thing first is to pull the CPU socket, and put a logic probe on each address line to see if any are pulsing while nothing should be happening).
The fuses on the power brick could definitely be an issue too - I've seen fuses go bad where they don't blow, but just break at the ends from age. If you pull a fuse and the end pops off - that could be the issue!
