I found it. It seemed temperature dependent, since the board would always come up to the mouse pointer when left for a while without power, but never when pressing reset or doing a quick re-power up. I used cold spray to check on the ICs, and hooray, when I spray UL8 (16L8 PAL) with cold spray...
I did some more work on it today and found a cracked inductor (no continuity) near the Nubus clock circuitry. I replaced that, tested the board and got video! Grey screen, mouse pointer. Hooray! Oh, wait, mouse pointer is frozen. Hit reset: Chime, no video. Powered it down, got a floppy drive to...
Hi,
for over a decade, I have owned a spare IIfx logic board (bare board, not in a case). Seems like it had not been worked on before, original (electrolytic!) caps. It chimed, but did not show any video and did not boot. A recap with tantalums and a thourugh board wash has changed nothing...
Sorry for a 'slight' delay in my answer. The mask ROMs seem to be pincompatible with 27C400 EPROMs used in Amigas. The TL866 programmer needs an adapter to deal with those, that's why I put the project aside and forgot about it. I will try it out as soon as I get the adapter from china - might...