A590 U5 Ram Controler

[Zac67]

U5 is always a 16L8A PAL. It's the RAM controller, so no memory expansion without it. Even getting the chip might get difficult, but you'll also need the code.

[Zac67]

Hmm - that's a shame. I don't think there's any way to fool read-protected PALs, otherwise the copy protection would be pretty useless...

At first glance I'd have thought that the A590 should start - maybe the RAM is accessed even in amnesia mode and the bus hangs due to missing ack. You can try bridging _RAMSEL to _DTACK (pin 5 to 18); not exactly nice, but it might bring at least SCSI to life.
(I always use a small resistor ~100 Ohms for bridging so nothing can smoke.)

[Zac67]

Well, somewhat. Does this help?