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I've just had a second PC power supply fail in the space of a few weeks - I went to switch on the PC and there's no response, no lights, no boot up, no disk spinning. Both were quite old units in separate PCs sharing a single wall socket via an extension block.

I'm wondering what can cause power supplies to fail. Are there failure modes that could cause them to fail so close to one another. Does switching on the wall socket and then off again quickly cause problems? It's probably just coincidence but I'm wondering what are common failure reasons for PC supplies and what can be done to reduce the chance of it happening?

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3 Answers 3

Both were quite old units in separate PCs sharing a single wall socket via an extension block.

This could just be normal wear. I'm responsible for about 220 PCs here, and the bulk of them are > 5 years old. Until I arrived last year we were replacing about 4 power supplies / month as a matter of course. I took the power supply budget and found some other money and doubled the rate at which we just cycle out old machines. Now we harvest the power supplies when we retire a machine. Old power supplies still die, but with fewer old machines it's a little less often and when they do I don't have to purchase the part.

It could also be the wall socket. You can improve things with a UPS, but the trick here is that a simple UPS isn't enough. You don't need much battery, but you do need one that not only does battery backup but also "cleans" your power even when it seems to be running normally. And that about doubles the price.

Does switching on the wall socket and then off again quickly cause problems?

If done over and over repeatedly, then emphatically YES!

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Why would it cause problems though if the machine is off? It doesn't draw any electricity thoug. –  JFW Oct 4 '10 at 14:46
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@JFW There's always electricity passing through the circuits, even when the machine is turned off... –  BloodPhilia Oct 4 '10 at 15:00
    
What would be the best way to prevent this then? There's no guarantee that someone else might unplug my desktop PSU plug unless I hide it in the nest of wires at the back of the room. –  JFW Oct 4 '10 at 15:06
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@JFW A UPS like I talked about in my 2nd paragraph. –  Joel Coehoorn Oct 4 '10 at 15:08

One of the things that used to cause me a lot of power supply failures was dust. The dust was insulating the components and trapping in excess heat. Once I started cleaning out the power supplies (be very careful!) with canned air I was able to extend the life of our machines another year or two.

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What can cause power supplies to fail? Bad wall sockets, spikes or drops in electricity, shorts in power cabling.

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