I have a tektronix 485 with power supply that shuts down because of a fault
on the balance node of the controller IC. This is a common fault that
appears often on threads in this NG.

The manual suggests opening pin 3 of comb "U" to isolate the -2950VDC
supply. When I do this, the inverter runs OK, the scope draws about 0.8
amps, and all of the LV power supplies are at the correct voltages. (The
fan doesn't run, however). So I have to find the short in the HV supply. Dug
into the scope and could find no shorted caps or on the transformer board
buried in the middle. The 15k resistor feeding the HV block was a bit
toasty and measured 33k so replaced it. No change in the performance. Caps
on the inverter board check out OK too. Is there a way to test the HV
multiplier block for shorts? Any suggestions on how to test the two 12,000
volt diodes on the xfmr board? Anyone ever sucessfully dig into the HV block
or try to replace it with a multiplier from another source, like a discarded
computer monitor?

Any help greatly appreciated.

Mark Palmquist