Gamma High Voltage Research RR Series

[Nick Peskosky]

Fusioneers,

I have been experimenting with a RR series 75kV/3.5mA reversible supply from GHVR but experienced a fault condition the other day during one of my neutron runs and can no longer see any voltage rise at either the digital front panel meters or the HV terminal. Does anyone have experience with these power supplies or have any technical documentation (test points/terminal block diagrams) that would be beneficial in troubleshooting? The supply starts and I can measure proper DC rail voltages off of the various internal regulators but I can see nothing but 60Hz noise on the HF transformer which drives the multiplier stages.

[Jerry Biehler]

I would start at the output diodes. You probably shorted one.

[John Futter]

Nick
check the fets that form the half bridge that drives the transformer
then check the waveforms coming from the smpsu ic probably a SG3524 or a uc38XX chip
download data sheet for this chip and check all pin conditions especially gate drive to the fets
I you think it is trying to work it could be a shorted turn in the transformer this will bring up over current input to smpsu ic and shut it down

for others looking at his thread if your output voltage goes up a little and stops rising it most likely a capacitor in the multiplier stage and the only way to test these is to subject each one to near its rated voltage. Just checking capacitance with a RLC meter will not find this sort of fault

[Nick Peskosky]

Thanks for the advice. The multiplier is unfortunately potted so I'm hoping its an IC or FET on the driver side. I'll run some tests and report back on my findings.

[Steven Sesselmann]

Nick,

I hope you have not damaged the multiplier, but if you have, this is what it looks like. Back in 2008 I blew up my Gamma HV RR series PSU, and it formed and arc through a tiny hole in the potting to the chassis.

There is a whole string of load resistors built into the unit, and in my case several of the load resistors were blown in half. Frankly the method used to sew together the multiplier is a bit primitive, there is no circuit board framework, the wires are just twisted together and soldered.

Steven

[Richard Hull]

Un-fedback, non regulated super HV supplies are doomed due to the natural weakness of the multiplier. Thus, they are very easy to blow due to only a moments inattention due to an arc, overload or accidental short. Multipliers with this many components in them are just itchin' to blow, the sign of a poor initial design and a failure to introduce a good intial high voltage to start with. I can understand the 3.5ma limit on current. Mostly it is a desire to reach a "price point"... To do this, they load a ton of 3 cent, 1kv or 10 cent 2kv diodes and 10 cent 2kv caps into a monster multiplier and pot it to avoid corona and keep the entire mess in a smallish volume.

There is just no need for more than a voltage quadrupler....ever! If there is, you are not doing a design correctly from the start.

With a massive outlay in cash and allowing for a huge volume in an oil filled giant multiplier tank more stages can be supported, but you are getting into proper professional supply territory.

Richard Hull

[Nick Peskosky]

Gamma's corporate office followed up with a general OM manual for RR series supplies which includes basic logic diagrams and pin out labels for supply's rear terminal block. My supply is considered obsolete based on their current production techniques and they said they would forward me schematics for the internal PCBs via snail mail... more to follow.