Tonight i've fixed up the Pleiads PCB that was in my little cabaret cab that was at Blackpool the other week - game died after Saturday but also had been reported to have graphics issues.
Symptom: Game booting to garbage on screen but music can be heard playing - or at least various tones continually playing.
Poke around CPU, clock running, RESET changing ok. Address lines aren't being driven high enough.
Replace CPU, boot progresses with a clear black screen and a line jumping about on it.
None of the RAMs are being selected properly. Traced back to an LS32 @ IC30, while diagnosing, comparator also told me IC19 (another LS32) was also problematic, pulled and replaced, both verified as bad out of circuit.
RAM /CS now changing state properly now but still no game.
Inspection of address and data lines on RAM shows no address activity, traced back to the LS157's at IC13, IC14, IC31, IC32 - all of which had broken STB pins disconnected from ground.
Visual inspection of PCB shows potentially some repair work from before had failed - or maybe this is factory? Checking against another PCB its definitely repair work as the other board has these nicely masked.
Patched all 4 of them and game now boots.
[tube]du1S0N1UJ10[/tube]
Symptom: Game booting to garbage on screen but music can be heard playing - or at least various tones continually playing.
Poke around CPU, clock running, RESET changing ok. Address lines aren't being driven high enough.
Replace CPU, boot progresses with a clear black screen and a line jumping about on it.
None of the RAMs are being selected properly. Traced back to an LS32 @ IC30, while diagnosing, comparator also told me IC19 (another LS32) was also problematic, pulled and replaced, both verified as bad out of circuit.
RAM /CS now changing state properly now but still no game.
Inspection of address and data lines on RAM shows no address activity, traced back to the LS157's at IC13, IC14, IC31, IC32 - all of which had broken STB pins disconnected from ground.
Visual inspection of PCB shows potentially some repair work from before had failed - or maybe this is factory? Checking against another PCB its definitely repair work as the other board has these nicely masked.
Patched all 4 of them and game now boots.
[tube]du1S0N1UJ10[/tube]
