Weird SE Power Issue (Intermittent Power On [Not Cold Analog Board Joints])

[mooseman]

I've got an SE I'm trying to get working and I'm a bit stumped, would appreciate suggestions.

Problem: from cold the system powers on and runs well. If restarted (via software or via the programmer switch) it boots fine. After running, however, if I switch off the main power and then switch it back on it's completely dead: no bong, no video, no fan. Let it sit for 20 minutes and it works fine again.

What I've done:
- Replaced all electrolytic caps & D2/D3 rectifier diodes on the analog board
- Replaced all electrolytic caps in the power supply
- Reflowed all solder pads for the plastic terminals on the analog board
- Replaced all electrolytic caps on the motherboard (not the root issue but I'm sure it needed it)

The good news is this fixed all the video issues and when it runs it runs great. The bad news is it's still got the flaky power issue. At this point I assume it's gotta be the power supply, right? It's got all new caps, any thoughts on what else goes bad on those or what to test? It has the Astec AA13800.

Normally I'd just try to find a newer replacement, but I'm doing this for a buddy and trying to keep things cheap. Suggestions appreciated.

 

[Builder68]

Have you checked that the AC power is reaching the PSU, just to rule out an issue with the power switch itself?

 

[mooseman]

It seems to be, yes. I'm getting power at the floppy drive port, but it's like 2V on the 12V line. I've tried flipping the switch a bunch of times and that's a no-go, which I wouldn't expect to be the case were it a mechanical issue.

Sure seems like something in the PSU is not happy after it heats up or charges up, but if it's not the caps I'm not sure what.