Some progress, I replaced the HV switching FETs and the standby current limiting resistor.
The PSU is now working and the unit boots.
I don't have acquisition working yet, but this is a big step forward.
While waiting for parts I've traced about 50% of the PSU input board schematic.
If I can find a mule PSU, I might finish the schematic off.
If anyone has a faulty PSU out there please let me know.

PS : These PSUs are quite complex and consist of 3 PCBs, but I'd expect that most failures will be in the input board.