So I haven't tackled U26 yet as I wanted some practice at removal/replacing chips. I did a few SOJs on a scrap board as practice before deciding to tackle the on-board RAM chips on the 575 board (due to the slightly mysterious failures post-reflow attempt). Unsurprisingly I did find and clean up some corrosion, presumably from some leaked electrolytic, around U22 and U19.
Unfortunately I think I have fried some of the chips - I'm back to the death chimes. I have re-checked continuity and for bridges (there was one bridge between address lines due to my fumbling and some solder resist that got corroded away). Is there a way to independently check these chips for proper functionality? They're NEC 424400-70 parts. I've spotted some on ebay.
I'd prefer to get the board back to a functional state before tackling U26 (so I can at least tell if I've fixed or killed it). Though I guess I'll have to admit fudgy-soldering failure at some point
As an aside: I assume it isn't a sensible way forward to get the board to boot just with a RAM SIMM? I imagine it'd be possible but would need CAS/RAS signals re-routing and possibly some other dodgy hijacking.