Power supply ElectroBoom moment (Patreon)

My HP 85645A 26.5 GHz tracker died while I was filming a video. To be fair, it never worked well and was shutting down randomly.  But now it would not start up at all. Switched power supply problem, less daunting than an RF problem fortunately. Complicated, custom, over-engineered supply with a lot of odd voltages. From the mid 1990s.  I got the middle finger from Keysight support : too modern, no schematics from Agilent like in the good old days, but too old, not supported for replacement parts or assemblies. So I had to do my best Ken Shirriff impersonation and reverse engineer it. About everything blows in this very unstable supply design: the fuses, the MOSFETs, the ICs... Very hard to debug when it's down, as everything powers and controls everything else in multiple entangled loops. And every time I get it stable enough to get close to the next fault, it knows, and something else blows. In the picture above I think I was getting close to the root cause. For a few seconds that is. I was not going to make a video on it, but now that it is turning into an epic debug battle against the forces of evil I probably will...