Interesting thread. I have the SeaSonic PS in one of my SE/30s and a SeaSonic in my IIci. To get the softpower to work, I had to follow the lead of @superjer2000 in a post in this forum that I can't find. It is a small board that got the softpower working fine in the IIci with the SeaSonic PS. If one was to out that same board in a SE/30 with the SeaSonic PS, would it have softpower?
Sorry this took a day! Hope this helps you out.
Panned out over board
Tried to get as much of the SMDs on the left, just before being covered by the floppy/HDD assembly. If you'll need pics of the SMDs beneath the floppy, too, I'll be working on the system later this evening.
Power supply caps in these systems (both 475 and IIsi) are known to fail. Sometimes they work after sitting, sometimes they work after a few times, sometimes they work with some heatgun action on the caps, sometimes they don't work at all. In some like the 475 (and LCs) you can often hear the power supply ticking as the thing tries to start and fails over and over again.
This is why I begged several times for someone to double check my pinouts, tables and wrap map. You CANNOT proofread your own work, period. The numbers on the rows on the IIsi pinout I've been using got reversed somewhere along the line.
Thankfully it wasn't A PCB layout screwup, That would have been a total loss. I have to all but start over. I only have to unwrap the 030 side, re-strip then re-wrap only that side from a corrected map.
edit: might have jumped the gun. The wiring may not be wrong at all? The numbers of the rows are inverted on one side, but the positions of all the connections remain the same? The numbers transcribed in the process of signal matching were mis-coded, but the spatial relationships IRL may remain intact. I'll look at it again in the AM . . . maybe.