Great stuff!
I have literally resoldered everything as I suspected some foul play with dry joints as well, but unless the issue is on the bottom PCB, I have literally reflowed everything, both with hot air and manually and nothing changed.
I have also tried with a freezing spray, nothing changes - so it doesn't seem to be thermal related, even if it starts after a while. If I leave it turned off for a night, it works for a minute or so before turning purple. Maybe it's dry caps?
I have a bunch of tools except for an Oscilloscope (I should buy one soonish), recently also got an ESR meter, so testing should not be an issue.
As long as the PCB has the spaces I just need to populate, it sounds doable
