I had my own share of HV problems on Barco 800/801. I have come to the following conclusions:
1) Failures of HV can only be due to the following (assuming the red scan fail light is not on by the focus controls)
a) Bad HV splitter
b) Bad Quadrupler
c) No +300V to the HV board
d) Bad HV board
Other lights on other boards have no bearing on the HV.
2) If the red LEd is on on the HV board, you have a HV shutdown problem due to too much HV or due to improper sensing of the HV feedback signal
The one I had uyesterdau was a bad quadrupler. Changed it, and the HV came back with the red light out. I have had exactly the same problem with a bad quad.
It's 11:00 PM. time for the quasi-tech to take a nap!...
Curt