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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?

TheCloudlessSky
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4 Answers4

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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.

Piotr Kula
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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.

Itzsquash
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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

Community
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zebonaut
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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.

Dave
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