Thinking about repairing a dead PSU

akio123008 · January 25, 2021

2 hours ago, ProjectBox153 said:

Where did you get the idea that I'm not going to use it if I get it working again? Also, I do have a good reason: I WANT TO. How much justification does everyone need on here? I'm sorry, but I'm just tired of everyone on here assuming I can't safely do something. Looks like I'll be going about this with less help than I hoped for.

Haha it appears that people are concerned about your safety.

Well you have been warned I guess. Personally I don't think working on a power supply is particularly dangerous, or at least not as dangerous as some people suggest. It sure isn't safe, but then neither is repairing any other mains electrical appliance.

If the thing is unplugged there's really not much that can go wrong. Those input capacitors will likely be empty after a few minutes. (surprise surprise there are bleed resistors in power supplies)

The actual hazard IMO isn't in working on the device, but in deploying it again after the fix. If you repair is dodgy, there is a certain fire hazard. That is where the real safety concern is. Therefore I wouldn't recommend operating the device unsupervised if you manage to get it working again.

Now then, what could be wrong with this power supply?

Given it doesn't show any activity at all, it's possible the power supply never even gets the power on signal as suggested by @Windows7geearlier in this thread. It's very hard to tell, it could be lots of things. Best bet is indeed to open it up for visual inspection, you may be able to see the problem.

I suspect it's very hard or even impossible to find a schematic for it, so you'll have to sort of build up one as you go along by probing with the multimeter (just checking what's connected to what and writing it down). It's a long and painstaking process, but you may just be able to diagnose it.

The hardest part of it is finding out what's wrong, the easy part is then fixing it.

ProjectBox153 · January 25, 2021

1 minute ago, akio123008 said:

The actual hazard IMO isn't in working on the device, but in deploying it again after the fix. If you repair is dodgy, there is a certain fire hazard. That is where the real safety concern is. Therefore I wouldn't recommend operating the device unsupervised if you manage to get it working again.

Exactly. If I ever get this thing working again am I going to put it into one of my utility machines that runs 24/7? No, I'm not stupid. Even if I was able to repair it and it was operating exactly as it should I would never trust it again. If a power supply in any of my computers starts to have issues I pull it out of service. I don't care what the machine is being used for as I'd rather all of my components stay safe as well as my house.

Windows7ge · January 25, 2021

Might as well add a little safety PSA (or whatever it's called) while I'm here.

If you can help it. Only put one hand in the PSU at a time. Don't touch anything grounded with the other and isolate your feet from the ground if you can. Do not use a anti-static wrist-strap either.

Why? Because that's how the high voltage/high current discharge from the capacitors finds a path across your heart. :3

Insulated screw drivers are also a good recommendation.

It's also worth mentioning you can discharge capacitors in a relatively safe manor by bridging their leads with an appropriate value resistor. The cap will discharge slowly with the energy being released as heat. If you don't have resistors handy the quick/dirty way is to just short the caps with a wire/screw driver. Not as recommended as the former method.