2246 no display/odd behavior
Ok so some updates:
I haven't found any previous posts that address my issues.
All voltages on the low side are in spec. Looking back at the ripple measurements in my first post I think they are all OK but a second set of eyes would be helpful. The p-p measurements seem high but there are very few points. The bulk of the points seem within the specs but there's some pronounced waveforms there that I don't know about being allowable.
I checked the ESR for all the electros on the power supply board - everything looks good (I used the Blue meter and tested in-situ).
Under the board I found a broken (lifted?) trace between C2244 and R2231. See here: https://imgur.com/a/bBWioVT I ran a jumper and re-assembled and no change in behavior. Still not display apart from a brief flash at power off and still the off behavior from the front LEDs where they don't power on unless I fiddle with the buttons.
There is a RIFA cap C2217 that looks a bit rough but not blown. I'm open to further suggestions or testing approaches. Still not sure if the two problems may be related or which I should focus on first. FWIW I can now get that PSU in and out in about 10 minutes flat... practice :D