On 28.02.2016 16:18, Cursitor Doom wrote:

[live power resistor procedure testing snipped]

Actually I did do this a while back without knowing the risks! As you
can see, I survived to tell the tale. All I was seeing was about 30V
of noise across that resistor but that was before I was informed of
the importance of hooking the supply up to a load, so the test was
probably invalid.

Also, even with a dummy load connected, the stray capacitance of an
oscilloscope, when hanging off the loose end of a power circuit with
some 800 to 900 V worth of HF on it, would probably cause so much undue
capacitive loading that the power supply circuitry would hardly handle
it. That may have been the reason why you just got noise (the overload
from the hanging scope may have affected the over-current shutdown of
the power supply controller). As I said, the proper way would be with an
isolated high voltage differential probe (such a probe would present
very little stray parasitics) or maybe with a well matched pair of
(identically compensated) HV probes in subtract mode.

Dimitrij