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Some background to my problem: My city had a thunderstorm last Monday and when I woke up, I noticed my desktop was turned off. I powered it on. It would stay on for about 20 seconds and then shut off. I figured it was overheating. I opened up the case and the plastic block that that HSF connects to was broken. I ordered a new motherboard and CPU combo (thought I would upgrade anyway). I installed everything last night.

When I power on the machine the power supply makes a loud hissing noise (not whining) that does not stop. I figured it could be something to do with the fan assembly. I did clean/blow some dust out of the power supply before installing the new motherboard (not too much, however). Additionally, last week when I was powering on the machine and it was overheating, there was no hissing sound. I've googled quite a bit to try and determine the source. I wasn't going to pop open the power supply as I figure it could be dangerous (is this true?). In my searches, I learned that it could be a leaking capacitor, but since I'm not an electrical engineer (I'm a recent CS grad), I wasn't 100%.

Could this be something electrical or something stuck in the fan? Is it worth taking the power supply into an electronics shop to fix or could I try myself?

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    Computer PSUs are so dirt cheap, just replace it.
    – Majenko
    Commented Jun 9, 2011 at 14:23
  • 2
    Snakes in a computer. :)
    – KCotreau
    Commented Jun 9, 2011 at 16:14
  • 1
    I have had it with these god-damned snakes in this god-damned computer!
    – Majenko
    Commented Jun 9, 2011 at 17:19

4 Answers 4

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Working many years in IT repairs I came across plenty of power supplies that did this - and only once in my whole life did one actually blow up and scare the living poo out of me!

The hissing noise is damaged voltage regulator- caused by failing components like you mentioned leaking cap ( does not actually mean its leaking- its just not charging to spec any more; hence-leakage- Such damage can also be caused by voltage spikes/dips or my favourite- lighting!) This over time causes damage to other components which causes a general failure.

The hissing noise is a bad sign and means that the power is not stable and could be potentially dangerous to the rest of your PC.

I suggest replacing it straight away. as trying to fix the problem would need extensive knowledge in electronics especially in AC/DC Conversion and understanding how each channel is split. normalised, regulated, blah blah blah..

And yes opening a power supply that has been recently plugged in can give you a shock- not lethal- but not pleasant either. You always need to discharge the large caps to the leakage part of the circuit.. which can be anywhere/ or grounded ground(meaning connected to your ground in your house!)

A few Dollar and your safe again.

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    It's not lethal until it is - and then it's too late to go 'oops - my bad'. Discharging the switching caps should not be done by someone with no experience in this sort of thing and not without the right kit. Having said that, a new PSU is not that expensive and you're right that a hissing PSU is telling you it's time to replace it.
    – Linker3000
    Commented Jun 9, 2011 at 15:52
  • Thanks. I'm going to suck it up and buy a new PSU. Although I don't have money bulging out of my pockets, I have a $20 gift for tiger direct that I can use towards the new unit. Thanks!
    – TheCloudlessSky
    Commented Jun 9, 2011 at 15:57
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    Yeah, I hate spending money unnecessarily too, but the last hisser I dealt with took out the motherboard and DVD drive too when it finally died.
    – Linker3000
    Commented Jun 9, 2011 at 16:20
  • @Linker3000 - Yup, as soon as I got home to check the PSU again, it hissed for 1 second and shut off - dead! So - I have to buy a new PSU now :) Thanks again!
    – TheCloudlessSky
    Commented Jun 10, 2011 at 0:31
  • I've had a little buzz from a PSU before.. it was a heat sink. I didn't think to avoid it a stupid heat sink...
    – Michael
    Commented May 14, 2013 at 4:48
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It may be the case that it is not even a damaged part, although this would be a bit unlikely for a PC power supply.

Related: https://electronics.stackexchange.com/questions/14256/what-component-of-my-phone-charger-produces-chirps-and-how-does-it-do-that/14257

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It’s most likely a dead or burnt out capacitor. This happens after long periods of time, but can also be caused by high voltage power that the PSU is not built to handle and in your case, a lightning strike. If you decide to open up the PSU, be cautious because there is always a possibility of an electrical shock. When opened, look for capacitors that look burned or broken. If there is blown capacitors, then I would recommend buying a new PSU. If there are no blown capacitors, then it might be something on the motherboard or other components.

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My first guess is that it's the PSU's fan's bearing or bushing. If you're going to take it apart, of course be careful. :) While it's open and on (and if hissing still) lightly press on the center of the fan. If the hissing sound goes away, it's the bearing or bushing. I haven't heard fans with bearings hiss, only vibrate, though. Bushings on the other hand, I have heard make bad noises.

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  • @Dave - Thanks for your response. I'll plan to take it apart this evening. Should I be extra cautious to not touch certain electronics? Could they still hold a charge?
    – TheCloudlessSky
    Commented Jun 9, 2011 at 14:12
  • Well, I always assume that things like power supplies can hold a charge even when disconnected for a while. I don't have actual data to support this, though, except for what the manufacturers say. :)
    – Dave
    Commented Jun 9, 2011 at 14:21
  • If you're going to touch stuff when it's plugged in, be extra super careful not to touch anything else. Remember, you have your live mains going in there. My recommendation would probably be to stop the fan from the outside when it's running by sticking something non conductive, like a toothpick or some bit of plastic, through the fan vent and stopping the fan.
    – pfyon
    Commented Jun 9, 2011 at 15:09
  • @Dave/TheCloudlessSky, the capacitors in there can store a significant charge (I don't know about lethal in most circumstances, but definitely enough to feel it). I've discharged the flash capacitor in a digital camera by shorting the pins with a screwdriver with some sparking. I guess this could damage the capacitor by discharging too quickly, but I've been told you can also short the live/ground pins on the plug (when it's not plugged in, mind you) with something and leave it a while to discharge through the built in circuitry.
    – pfyon
    Commented Jun 9, 2011 at 15:15
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    Just a general comment about electrical shocks and their lethality: Everyone is different and some people are more tolerant of shocks that others, some people have drier skin and so the higer resistance reduces the shock current to a less harmful limit - and some people have an as-yet-undetected rare heart condition or particular susceptibility to shocking that makes itself apparent as soon as they touch the bits and pieces. There are too many variables and it's not worth the risk to find out what type of person you are.
    – Linker3000
    Commented Jun 9, 2011 at 16:00

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