[MIPS]

Whoever said it's not just a diode is right and wins a cookie.
I did a suicide test and with the diode unhooked I ran it line voltage with a foot pedal to briefly power it.
We got high voltage, too much in fact. B+ peaked at 190v on the meter, so the power supply is not regulating and that is why the diode went.
(also after this test I checked the HoT and the spike didn't kill it)

I'm looking all over the primary side and the feedback area of the power supply. I see no drifted resistors, no shorted capacitors or diodes and the B+ adjustment seems to not be open. No obvious sign as to why it wouldn't be regulating.