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Problem:
Game is dead, no image on screen, 1 and 2 player start are solid lit
Troubleshooting/dianosis steps:
- Tested RAM 0x0000 - 0x00FF and 0x0800 - 0x08FF on Fluke long RAM test - OK
- Tested ROMs against known good signatures - OK
- Probed !RESET pin on CPU, it's constant low
- Disabled watchdog, RESET goes high, but game does not work
- Used fluke to write to watchdog memory address, noted that when writing the reset pin changes to high but stays high even if I stop writting to it.
- Noted HSYNC does not transition
- looked at schematics, tested 74LS74 at P2, found pin 5 was low, pin 6 (opposite state of pin 5, transistions) replaced chip, new chip pin 5 is STILL stuck LOW
- Pulled out 74LS74 tested pin 5 and without chip and found it still low
- Looked at schematics traced pin to pin 2 of N2 and M2, removed those chips
- Found pin 5 is STILL stuck low
- manually traced pin 5 on lower side of board to 72LS02 @ N8, snipped pin and found that pin 5 of P2 was no longer stuck
- resocketd and replaced the 72LS02 @ N8 and the 74LS163s at N2 and M2
- RESET is no longer stuck low (is high now) and HSYNC is transistioning
- game boots up passes self test and seems to work, graphics seem to be black and white only, need to look into that whether normal or not
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