Well, I've spent the entire weekend on this thing and it's starting to drive me boing! I replaced the oscillator, no change, replaced the 2 resistor packs near the ROMs, no change. The old ones tested OK, which I expected as I've never seen those go bad. BUT, pressing on the ROMs, either one, makes the machine boot, as does heating them. So I replaced those sockets, and it is more reliable but after a long power-off period it still won't boot, pressing on the ROMs quite firmly makes it boot. The sockets are new and connections seem to test out ok, and it always boots with the built-in 68030, so I think those are fine. I looked all around that area and see no issues. But, how many layers is the 9.2 rev A3000 board? Could it be a bad via or a trace in the board that's wonky? So frustrating!