Check that "hot" on mains goes first to the fuse, then the on/off switch. Not neutral, as some are wrongly factory wired.
Check continuity between the wand nozzle metal can, and mains earth-ground. The nozzle is stainless steel and usually the GND wire is loosely wrapped around a hole, making a flaky connection. You need special solder.
Ensure the ground wire from the back of the GX-16 connector goes to earth-ground, usually at a second bolt on the power transformer.
I drew up a
schematic of 858D06.PCB and wand including the original on/off switch safety mistake.
Best to never leave it plugged in when you are not using it.
The wand connector on the front panel has hazardous live present, so never mess with it unless the unit is unplugged.