PC power supply fan

Quick question for you tech junkies: I have an old Dell PC, circa 2002 or so. It’s been shutting itself off lately, and I think it’s due to overheating.

I opened it up, and sure enough, the CPU cooler fan is not starting up anymore. But the fan on the power supply doesn’t seem to be starting either. It does boot up, so I know the power supply works. So my question is, should the fan built into the power supply come on right away, or is it normal that it doesn’t start up when the system comes on?

For what it’s worth, same question for the CPU fan. I assume it should start going when the system turns on… right?

Right. Replace both fans.

Normally, both fans should spin up at power on. However, I have seen “smart” systems that only spin up the fans when the temperature reaches a certain limit, and shut off again when the temp drops enough.

This is correct, the fans should however kick on within a few minutes one way or another. The really cool ones will adjust fan rpm looking to keep it at a certain temp.
Only issue with PS fans is sometimes they are soldered to the board and will require you to splice the fan power wires. Sadly, even good supplies are often not worth the effort if you can’t do it yourself. If you need a cheap replacement, I highly reccomend www.amamax.com. They sell dirt cheap power supplies and I have gone through dozens of them in my shop without any problems.


Still, when the power button is pressed and the system begins to boot, I can’t think of any sexy temperature/power management stuff that keeps all the attached fans from spinning full speed for a few seconds.

However, I think it’s odd that you’re not getting any POST messages regarding dead fans - especially the CPU fan. Of course, I’m not sure I’ve ever seen a power supply that had its fan blow before the actual PSU blew.


I’ve had three ps fans fail on me without the PSU failing over the years. The first one the fan’s plastic hub physically split and the fan went BRAAAPPPPPPPPPPP as what was left of it tried to keep spinning around. The other two died a silent death.

Some motherboard come with a monitor utility that will pop up a warning on your screen if the CPU fan fails. You can also usually monitor the speed of all of the fans and the current motherboard and CPU temp and alarm on any problems.

Thanks for all the replies. I was going to go ahead and replace everything myself, then I thought about all the crap I have to do over the next few days for Christmas and work, and decided to take the easy way out. It’s at the local computer shop now, where they have CPU fans and power supplies and nice young men in stock and willing to fix it for me.

Shoulda done that in the first place anyway. I can’t think of anything I hate more than mucking around with hardware.

Dang. My local computer shop doesn’t stock those. By the way, where in the UP did you find a good computer shop? My folks spend time near Iron Mountain, and have been trying to find one.

Beware that some Dells use custom PSUs. And messing inside a PSU is not recommended. Have you checked the fans for dust? Give them a squirt of compressed air.

What’s wrong with messing about inside power supplies? Sure, those big caps can hold dangerous voltage for years…so don’t go grabbing on to their contacts. Replacing the fan is unlikely to require you to get anywhere near them. If the fan leads are soldered straight to the circuit board you can just cut them and splice onto them, no need to pull out the soldering iron. But there’s a decent chance it will terminate on a little two or three pin header, anyways. The fan is just a 12vdc circuit and not dangerous in the least.

It’s not the deliberate touch that concerns me: it’s the accidental slip.

Ditto. Not that many, but the fans died and the PSU lives on. It was a simple swap and splice to repair.

I don’t mean to suggest anyone should ignore the potential danger here, but when you open up a power supply, you will ordinarily only have access to the top of the circuit board (unless you take it apart further than just cracking it open). The dangerous bits are on the bottom of the circuit board, where the contacts for the capacitors stick through. If all you do is take the top off and replace a fan, is should be damn near impossible to cross the cap contacts even if you try. You’d have to wiggle a couple thin strips of bare copper down beside the board and try to get them to curl around underneath and touch the relevant contacts, or something like that. So don’t do that. :stuck_out_tongue:

Note: if your power supply isn’t configured conventionally and the first thing you see when you open the case is the bottom of the circuit board, proceed with extreme caution. :slight_smile:

My experience is that PC power supplies can be a real bear to work on - they often have wire bundles tie-wrapped to the case, and everything fits together like a Chinese puzzle box.

FYI, it was both the fan on the power supply and the CPU fan that were out. They replaced them both. They had parts in stock, and charged me $100 for the whole shebang. Money well spent IMO.

Apt description, considering where they’re made. :smiley:

FWIW, I don’t advocate messing around inside a PSU. If the fan failed, odds are good that the PSU itself has been heat-stressed enough that something else inside is getting ready to fail, and will spite you by failing ten minutes after you put it all back together.

Yes, fans are cheap, but PSUs are also cheap, as long as you’re not faced with something odd or proprietary like a Dell or Sony Vaio.

Not bad, especially since I’m assuming that includes labor. For the time involved and the whole puzzle-box issue, I’d charge $100 in labor alone to crack open a PSU and replace parts. I’d wager the final bill broke down something like:
fan: $10, PSU: $45, labor: $45.


fan: $15, PSU: $35, labor $50