I thought I would share in case anyone else runs into the same problem. I just received a new Framework 12 DYI, added RAM and SSD and tried to fire it up and … nothing. I read the notes about RAM training and left it for a couple hours while I did other things, nothing, though after long enough waiting the fans kicked in.
Short story long, I had a USB docking station on my desk and hooked up to that I could POST and install an OS. In the afternoon sun beam I could see that the display panel was actually working without backlight. The connections from the display to the motherboard were fine, and reseating them didn’t help. I then dismantled the panel and found one of the two connections on the back was partially unseated.
Reseating that connection immediately resolved the problem. Bummer that it was loose from the factory but the ease of disassembly saved a warranty return. 
Hope someone else finds that useful.