BOARD NO:     0089
GAME:         Karate Champ
MANUFACTURER: Data East
DATE:         1984
HARNESS:      DECO-S

SYMPTOM (13/04/96)
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ROMS were missing, but were replaced and verified as correct. The game generally failed to initialize, but would occaisionally boot and run correctly. 

SOLUTION
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Flexing and tapping the board had no effect. Changing the inter-board ribbon cable had no effect. With no physical intermittence evident and no other fault evident when the game was up and running it was time to look at the power-on-reset. Tracing the reset lines from both processors revealed that the Z80 closest to the back left corner of the board was the master, with the reset for the sound Z80 fed from a latch controlled by the master. Tracing the master Z80 reset back through an LS04 up until it terminated in a custom SIL module in the front left corner didn't reveal anything suspicious. To veryfy that the power-on-reset was the problem, a pulse injector was used to pulse the reset line on the master processor. This started the game correctly every time. Disconnecting the switched mode supply and re-connecting it (using a dummy load to maintain the supply voltage) always started the game where as switching the supply off and on didn't. In the end, the board was declared good and the fault put down to the switched mode supply taking longer to stabalize the voltage than the game's reset period could accomodate, since the gane was probably designed with a linear supply in mind with quicker stabalization at power on. (or, my supply is slow to stabalize - take your pick).