After finally cleaning the workbench so I can see it, I decided to drop a new motherboard into an old PC. A ten minute job.
Tested the power supply / mobo on the bench, worked fine. 🙂
Put motherboard/PSU in case, hooked everything up, and it won’t power on (UGH). 🙁
Unplugged everything, nope. 🙁
Pulled mobo out of case, it powered up.
Slapped some electrical tape on mobo where screws go in, mobo back in case, nope.
removed motherboard, it works.
Inspected power supply connector, touched up solder connections, put mobo back in, nope.
with mobo powered up, put mobo into case….mobo shut off half way there! :{
jiggled power supply connection, mobo shuts off…hmmmm.
inspected power supply connection…looks fine.
gently tugged all wires of PSU connection…AHA :)…black/brown wire breaks off in hand..
Extract pin from connector, resolder wire, done. v/
One hour later, new mobo installed.