Hi
I went through and did a lot of static checks on the power supplies to make sure there were no obvious broken parts.
The power supplies have a cascading protection scheme starting with the 50V supply. The +24VDC supply requires a 50V input to the reference. If the 50V supply fails and goes to zero, the 24VDC reference is zero and the 24VDC supply goes to 0VDC.
The +12VDC supply reference also depends on the 50VDC supply. The +5VDC supply reference is driven by the +12VDC supply. Other supplies also have dependencies.
As a result of all this interconnection, if one fuse blows, multiple power supplies drop out. It looked really bad, until I dragged out the schematics to see how everything works. Once I had completed static checks of the key components in the power supplies, I refitted/replaced the fuses as required, and flicked the power switch. It all burst back into life again as if it was just another day.
The +5VDC power supply has some interesting features, if you are a power supply geek. It runs 2x 2N3055 power transistors in parallel because one was obviously not enough. That is a lot of power. The transistor that supplies the base currents is itself a power transistor. Being all linear power supplies, there is a lot of waste heat.
The newly fitted heat sinks are definitely doing their job. The heat sinks combined with the fan controller are working well together. I can't quantify how much heat is being dumped by the heat sinks, but it is significant. I have tuned the fan controller to start accelerating from a low base speed at 25 deg C, and go to full speed at 50 deg C.
With the power supplies now fully operational, I checked the repair to the CRT power supply (new HV cap). The good news is that the symptoms consistent with a failed HV capacitor have gone. The bad news is that the power supply output is unstable, consistent with arc-over somewhere. That brings the tally to 4 defective/replaced components and at least one more to discover. I now have a used HV 1000:1 probe so I can now poke around to see new things I could not see before.
Three of the rotary switches were loosely mounted, so I tightened those up.
To the HP employee that left the message "FIXIT" 55 years ago please note, where ever you are, I am trying.
So the next step is to figure out where the remaining HV fault(s) is. So far no magic smoke has been observed during test flights.