A Gyruss bootleg shows a false greenish color in the title graphics as well as has a flickering pixel line on top of the screen.
The false color is most likely to an errorneous PROM (as mentioned in a repair log over on arcadeotaku).
Reading out the PROM shows that it has a wrong value in just one byte location.
Burning a new PROM and inserting it brings back the correct color.
Still the flickering pixel line is there.
A visual inspection shows a damaged capacitor connected to the VCC pin of a 74LS257 (which should be a74LS157 according to the pcb layout).
Replacing the damaged capacitor with a 300 (30pF) one on the other side of the pcb rids the game from the flickering pixel line.
Gyruss graphics working 100% again.
The false color is most likely to an errorneous PROM (as mentioned in a repair log over on arcadeotaku).
Reading out the PROM shows that it has a wrong value in just one byte location.
Burning a new PROM and inserting it brings back the correct color.
Still the flickering pixel line is there.
A visual inspection shows a damaged capacitor connected to the VCC pin of a 74LS257 (which should be a74LS157 according to the pcb layout).
Replacing the damaged capacitor with a 300 (30pF) one on the other side of the pcb rids the game from the flickering pixel line.
Gyruss graphics working 100% again.
