Board was in very good condition :
But on power up it gave only a solid black screen and nothing more hence deeper troubleshooting was needed.Probing the main CPU/RAM/ROM circuitry revealed that the lowest address line (A0) was stuck high on the three program ROMs and nearby RAM :
ROMs and RAM are addressed by the main CPU (a custom Z80) not directly but thru some 74LS244.I traced the stuck address line back to an output of the 74LS244 @IC124 which, according to my multimeter, was shorted to +5V :
I was almost sure the TTL chip was bad (it was from Fujitsu too) hence I removed it but it turned out to be good.So there was something else shorting the address line to VCC preventing the game to boot.I flipped the board over and traced on solder side the shorted address line back from the ROMs/RAM.While I was following the traces I came across this :
A close-up under the microscope :
A VCC pin was bended on the nearby trace of the address line peeling-off the solder mask and causing the short, unbelievable!I promptly straightened the pin and board sprang to life :
I played some games, no further issues were present, board was 100% working.Another successful repair accomplished.
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