At the request of a friend I was asked to fix the inverted screen issue with Athena.
An hour or so at the hands of the MAME debugger and a couple of false attempts the resulting patch is a simple two byte change to the rom.
In rom up02_p4.rom change these bytes. (actually, the patch swaps them around)
$029e to $48
$02a4 to $3e
Burn a new 27c128 rom and its done. Since we are swapping two bytes, the checksum doesn’t change.
Edit: Tested on a real pcb. Works perfectly as expected 🙂