[ziml77]

I see they have the exact same frustration with the results of trying to research how to safely work on a PSU as I've had. I know there's plenty of info out there about working on CRTs; are the caps in PSUs really more dangerous than that?

[duskwuff]

Modern computer power supplies are far less dangerous than CRTs were.

CRTs were dangerous because they used extremely high voltages (often as high as 25 kV), and that voltage was often present on the CRT itself, which acted as a capacitor. The capacitance of the CRT was relatively low, but it still stored enough energy to be very hazardous. There's ways to safely discharge them, but you absolutely need to know what you're doing and work with one hand behind your back.

The voltages in a modern switching power supply are much lower (typically no more than ~1.5x line voltage ≈ 180V), and the capacitors usually have "bleeder" resistors which will discharge them to safe voltages within a few seconds. I'd still give one a few minutes before touching it - and maybe check one or two of the bigger capacitors with a multimeter - but it's still much less dangerous.

[userbinator]

The main danger with CRT HV is not the HV itself but what the shock will make you do, such as jump and cut your hand on something sharp in the chassis, or even crack the neck of the tube, or fall and hit yourself. There is very little current available, especially if the set has been off, but it's comparable to a very painful static shock. Instead, the "low" voltage B+ supply is far more dangerous when the set is on, as that is basically rectified mains.

[analog31]

Beware. I took a poke from the focus anode of a CRT when I had a job repairing mainframe terminals in the early 80s. I thought I had discharged it, but apparently I didn't.

I had to sit down in a quiet room for the rest of the work day, before I could function again. It was probably 13 kV, which was typical for monochrome displays back in the day.

Also, anything in a CRT television can kill you because TV's tended to have a "hot" chassis. The repairmen always plugged a TV into an isolation transformer so they could ground its chassis while working on it. There's a lot of counterintuitive things about those old electronics due to clever cost reductions.

[userbinator]

The focus anode is lower voltage (~1kV) but its supply may be capable of higher current.

[analog31]

I might have gotten my terms mixed up, but it's the suction cup thingy on the side of the tube. And it was disconnected, so the poke I got was from the charge built up on the capacitance.

We had a procedure for discharging it, which I must have bungled.

[JonChesterfield]

It hurts if you poke the wrong part with a finger while it's live. I'm still here, ymmv.

[mrlonglong]

I was once told about a chap who got his ring finger blown off because the spanner he was holding inadvertently made contact with a car battery terminal and the engine. Ouch.