easy fix for PC's power supply?

PSU on wife’s PC died yesterday. I was able to get it running again by using the PSU from my old PC, but the harnesses on that one are too short, so the PSU has to sit on the desk next to the PC with the panel removed.

Two options for restoring her computer to the nice buttoned-up box it used to be:

  1. fix her old PSU, or
  2. buy a new PSU, or
  3. buy a new PC.

I gather PSU failures are relatively common, which suggests that there might be a relatively common point of failure within the PSU. I have a history of ignoring labels that say ‘NO USER SERVICEABLE PARTS INSIDE’, and so I’m quite happy to take the old PSU apart and replace whatever component may have crapped out, provided this is feasible. She hasn’t been thrilled with this PC though, so if I can’t fix it for $20 and an hour of my time, we’re prepared to just buy her a whole new machine.

So…what component in the PSU is most likely to have fried, and is it reasonably easy and cost-effective to replace?

Read the label

No User Serviceable Parts Inside

You cannot repair it. Get a replacement - they don’t cost much.

i count differently from you.

you could also splice in wires in the middle of the harness to make it long enough.

internal PSU repairs aren’t easy or safe if you aren’t a skilled technician.

price a new PSU. the cost may be such that repair of any sort isn’t worth it. keep this old PSU as a spare for emergencies to use like you have.

Cut the cables from the old PC and replace those on the replacement.

Most likely, you’ll have to replace a lot of parts since when a SMPS fails, a chain reaction of failed parts is often the result; for example, the switching transistor fails, which in turn burns up the current sense resistor connected to it, then the controller chip and associated components (often its more like an explosion than just “burning up”) - all of which have to be replaced or it will most likely fail again (plus, as one who has made numerous SMPSs, you NEVER want to test them by plugging them in after building (or repairing) one; I use a power resistor in series with the DC power line to limit current as a first test, while also monitoring the transformer’s output voltage to ensure proper switching and regulation). The same goes even if you just find a blown fuse, since replacing it very well could make things worse unless the fuse just opened up. Not a job unless you are skilled in this area (even if you are an electronic hobbyist unless you regularly make mains-powered circuits like this).

You can also buy extension cable for the PSU. I just checked Newegg and it looks like the cable should be available for about five bucks or less.

Then I’d go for that, too.

Attempting to fix the PSU is just going to destroy the rest of the computer the instant you turn it on. Unless you’re really, really, really good. But you can get a PSU for like $35, so why take the risk?

A power supply for a basic desktop is so cheap that the time spent driving to the store and buying it is probably a more significant than the actual price tag.

Piling on, but yes. The power supply IS the user-replaceable part. In my extensive experience, they’re the second most common component to fail (after video cards and before magnetic drives) in a PC, and they’re cheap and easy to replace. The couple failed ones I’ve opened always have burned sections on the circuit boards, so “fixing” them would be pretty much out of the question.

I’d use it as an excuse to buy a new PC, though, if the primary user of the system doesn’t like it, anyway.


Read my post, which says I don’t really care about labels like that. Michael63129’s explanation of why it’s difficult and what the risks are is very helpful, but a blanket statement that says in essence “don’t worry your pretty little head about what’s inside that mysterious box” is not.

Dewey Finn, thanks the extension mention. If it’s really that cheap, then it’s hard to justify cutting/soldering to splice in extra length. I’ll have to see how much my wife hates her current computer, and whether she wants to spend $5 for a PSU extension cable, or a few hundred for a new PC. :smiley:

No, you don’t want to buy cheap PSUs - those are the kind that are much more likely to fail, especially in ways that could damage the rest of your computer, or so I have heard. Then again, the last computer I had ran for 8 years on a cheap generic PSU (whatever Compaq had on hand) and the PSU still worked after it died (although I didn’t keep it, being only 200 watts, I just used it for parts; internally, it looked better built than some other generic PSUs, including one I found recently that claimed to be 300 watts but probably couldn’t produce half that, not surprisingly, there were burned parts in it).

Here is an article that should make you think twice before buying the cheapest PSU you can find.

For the first PSU, rated at 500 watts:

For the second PSU (750 watts):

And for the grand finale (supposedly 420 watts):

None of the three PSUs tested were able to supply more than half their rated load without failing, two of them permanently; long-term reliability is just as suspect (efficiency was also very low even at these levels, good power supplies will be 80+ certified). Now again, you’re probably less likely to find this with low-end (wattage) power supplies, since the above examples seem to be supplies which were given power ratings beyond their design capabilities (including increasing the overcurrent limits in the latter two, thus the failures).

I agree that you should never buy cheapest finest dodgy PSUs. But these days, there are plenty of quality PSUs from reliable manufacturers for under $50. For example, this basic Antec power supply is $35. It’s not like when I built my first PC 10 years ago, and any PSU that cost lest than $100 would probably start a fire. (Though that still applies if you try to buy one from, say, Best Buy).

I dunno about that Best Buy thing. Last power supply I bought was a mid-range Antec at a Best Buy. Unless the major manufacturers are putting different stuff into their brick-and-mortar and on-line retail distribution chains, a local store shouldn’t be a huge disqualifier. Brand rep is important, as is mostly-unbiased technical reviews. But brick-and-mortar shouldn’t be a problem, other than higher cost plus sales tax if applicable.

I have a very good quality power supply in my computer that I do use for gaming. I would not spend that money to replace a power supply in an older computer that is not used for power intensive activities.

At a local computer supply shop I can pick up a nice, warrantied, name brand power supply for $40 Canadian. It would probably be overkill for this purpose.

Open it up and see if there are any obviously damaged parts inside. I used to repair PSUs for desktops and printers in a foreign country. People would bring their equipment over from the US, forget to flip the switch on the back from “120V” to “240V” and fry up the power supply. Almost 100% of the time it was an MOV that blew, and you could solder in a new one in under five minutes.

Once you get past the protective circuitry (MOV and fuse) though, I wouldn’t suggest fiddling with much else. Like others said, you could fry the motherboard. But it’s worth opening up to see if there is a fuse or MOV blown, because they are easy to replace and will save you a lot of money.

Basically I’m referring to the high prices and lack of selection in a lot of brick-and-mortar shops like Best Buy. I just checked their site, and they basically have seven models in any nearby stores. Four cost upwards of $115. Two are cheap no-name brands which I would not trust at all. They do sell a cheaper Thermaltake PSU, which looks like a fine choice but it’s $55 whereas Newegg sells it for $35 (including shipping and a rebate).

But, in an emergency, $20 isn’t a horrible “get it right now” tax.

And I guess that’s the point I was making, too. If it’s the same brand, it comes down to “now” vs “cheap”.

Given the original scenario (computer is working OK with a “borrowed” PS), “now” is probably less important, so driving to a brick-and-mortar is either being old-fashioned (disliking online sales) or really fond of a particular brick-and-mortar place… and I’ve never heard of anyone being that fond of Best Buy :stuck_out_tongue: