That actually might be a problem with the power switch. Those things are meant to switch live mains -- intentionally connecting the in and out of two legs of mains power. There is absolutely no reasonable explanation for you to have contacted live mains through the switch itself unless it's defective, or you went out of your way to screw up the wiring. (Like, connecting one of the mains lines to the outer metallic shell of the switch.) Another possibility is that you shorted the mains returning from the switch somewhere, like a chafed wire or part of the PCB making contact with the PSU case.

Either way, chances are the net effect is that it's shunting AC to the case, which is grounded, and may be having trouble starting with part of its input power flowing straight to ground. Hence the whining. But that's just a guess.

SirNickity wrote:

That actually might be a problem with the power switch. Those things are meant to switch live mains -- intentionally connecting the in and out of two legs of mains power. There is absolutely no reasonable explanation for you to have contacted live mains through the switch itself unless it's defective, or you went out of your way to screw up the wiring. (Like, connecting one of the mains lines to the outer metallic shell of the switch.) Another possibility is that you shorted the mains returning from the switch somewhere, like a chafed wire or part of the PCB making contact with the PSU case.

Either way, chances are the net effect is that it's shunting AC to the case, which is grounded, and may be having trouble starting with part of its input power flowing straight to ground. Hence the whining. But that's just a guess.

I couldn't tell you if the PCB was shorted to the case or not. For that, I'd have to take it apart again, something I don't feel like doing at the moment considering that I probably just took 60Hz 110V in the arm, which isn't that bad, though I've read on things in my IT class that 110 60Hz can apparently kill you.

I'm unsure of it having that scale of danger, but it doesn't feel good, and it scares me every time.

To be fair, the PSU was outside of the case at the time, so it didn't have the case to ground to. I'm not sure how much this changes, if anything at all.

A 9v battery can kill you, under the right circumstances. Don't let current cross your heart to find ground. That's the biggie. Pretty much everything else just tickles a bit.

If your AT power switch wire bundle is four wires, then the fault is either the switch or the switch cabling is abraded and touching the case somewhere. (Possibly the switch terminals, if they're exposed at all? Usually they're covered by insulated spade terminals or soldered and insulated with heat-shrink tubing.)

If there's a separate ground wire (usually green, and usually with a ring terminal that you're supposed to screw to the case somewhere near the switch) along with the four switched mains wires, and that wire was connected to the chassis, then the PSU could also be at fault -- something in the PSU is dumping mains to the chassis ground.

Basically, current got to the case, which is supposed to be grounded, and that's supposed to trip the breaker. That's WHY the case is grounded (that, and secondarily to eliminate parasitic charge build-up, and shunt HF noise to ground.) Live mains should NEVER be exposed via the switch, and if it is, the switch needs to go. A new PSU is likely to cause the same issue if the switch is defective.

Volts is not what determines "Killing Power", it's amps.
A static spark (carpet spark) is 20,000-30,000 volts but low current.
https://www.asc.ohio-state.edu/physics/p616/s … al_current.html
Most actual authorities agree that 0.1 amps is "THE" number for probable death and that's what most electrical safety Standards are based on.

I actually read the incident report for that nut that killed himself with a 9v battery. (Required reading for my job.)
He used meter probes as needles and stuck one into a vein on each arm. Supposedly he was trying to measure the resistance of the human blood stream but the meter he used puts out 9vdc from the battery to test resistance.

Wet human skin has at least 600 ohms resistance. (Realistically more and that doesn't count body resistance, just the skin.)
600 ohms and 0.1 amps -> 60 volts so we administratively controlled (had extra rules) for working on anything live over 30v.
The dead 9v nut above bypassed his skin resistance by putting the probes directly in his veins.

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Plug the system into a power strip with a switch.
Use the power strip switch to turn it off and on for your various voltage checks.
Turn it off (at the strip) any time you have to touch something other than with a probe.
.

We generally treated 24V as the threshold for the same reason. North American GFCI manufacturers base their trip thresholds on the 16mA muscle release limit (variously set at 4 to 6 mA) while the limit elsewhere is usually based around the ~50mA fibrillation/respiratory arrest threshold. They're designed to trip fast enough that energy delivered into the body is not dangerous.

Other factors come into play, of course. A shock delivered arm to arm through the chest cavity will be more dangerous than one which passes from one arm down one of the lateral sides of the chest and abdomen. This is why some shops will advocate keeping one hand in your pocket while working residential voltages.