Circus Charlie Repair Logs

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Repairer: Paul Swan

BOARD NO: 0066
GAME: Circus Charlie
DATE: 1984

SYMPTOM (27/04/96)

White virtical bars on background.


Using a pulse injector on the ROM data pins indicated that EPROMS 4A and 5A held the background. The data bus of the two EPROMS were bussed together as was the address bus. Checking each data pin with a logic probe indicated that all the data pins were pulsing. Using a pulse injector on each data pin revealed that data bit D4 had no effect on the video when stimulated and this was selected as a candidate for further investigation. The EPROM data bus outputs were traced to the inputs of an LS273 octal flip-flop. A logic probe indicated that the EPROM D4 was being input to the LS273, but the output was always high. The other inputs and outputs were pulsing normally. Replacing the LS273 fixed the game.