I would suspect the 7404 at Z11.
A logic probe would help you know with certainty.
You can also "diode test" that chip with a meter.
Meter on diode check.
Board out of game or connectors removed.
Red on lower left pin.
Black on other pins one at a time.
.4-.7 should be the reading on each pin except the upper right pin.
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Chris Hibler - CARGPB #31
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