Professional software development, amateur BMW tinkering, old arcade game stuff


Midway Mortal Kombat arcade pcb repair

Game booted fine, but everything was tinged red.


Luckily schematics for this game are available so this was a quick fix.  Schematics show the palette RAM connects to a pair of 74ALS574 chips, which go to a pair of 74ALS541 chips which then go to a resistor network to form the analog RGB output.  A logic probe showed one of the inputs at U3 was dead, but the corresponding output on the palette RAM was pulsing away.


So what looked like a tiny scratch on the PCB surface was actually a deep gouge that had completely disconnected a trace line.  This was patched and the PCB 100% working again.

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