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CPU system fan may not be functioning properly.

Posted on 2008-10-27
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Last Modified: 2012-05-05
PC: custom build:3.4GHz intel Pentium4, Gigabyle 8IPE775-G, 1GB RAM, pretty standard components.

This PC (of a client) stopped starting, and I could not get it to start, so took it to my favourite techos. They said that  the PC is OK, just needed a clean, which they did.

Back at my office now, I did some updating and maintenance before I am due to return the PC tomorrow. During all of this the power supply area was getting hotter, in the end almost too hot to keep a hand on it. (When I took the cover off it was hotter.)

I looked in the BIOS: current CPU temperature = 70 C, current CPU fan speed = 2720 RPM,  current CPU system fan speed = 0 RPM."
I enabled the "System fan fail warning", and when I saved the settings, an alarm sounded until I went back into the BIOS and switched it off".

Does anyone have an idea of what is wrong, and/or how to fix.

Thanx, Rosemary
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Question by:rfs777
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by:slinkygn
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Sounds like your system is telling you a fan has failed! :-)

One of your case or power supply fans is dead or otherwise defective and needs to be replaced, most likely.

Usually a simple matter of buying a new fan of the same size and voltage requirements.  They're all over the place.  Ebay, Digikey -- you might even be able to find the right size at your local electronics store.
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by:smiffy13
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The system fan is the case fan. Many cases don't actually have a case fan, which would explain why yours is saying 0 rpm. By turning on the system fail warning would obviously cause the alarm if you don't have a case fan.

Your power supply shouldn't get that hot. I suspect that the fan inside the power supply isn't spinning. You can usually see this fan throught the grille at the back of the PC. If you can see it's not spinning when you turn the power on: then you need to replace the power supply unit (PSU). Most PSU fans are not replaceable, so you'll need to replace the whole unit.

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by:rfs777
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Thanks for your comments so far.

Smiffy13, the fan in the PSU is spinning when I look at it. Is there anything else in the PSU that would cause it to generate heat?
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by:slinkygn
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The PC is a custom build.  It is remarkably typical that builders get the power fan and case fan headers confused.  And it's remarkably easy to check for a failed or failing fan.  If they're all spinning,  just take a piece of paper and try to stop the fan with it.  They should all have enough torque to basically ignore a piece of paper.  If there's any slowdown, you have a defective fan.  And if you're having overheating issues, you should be checking them manually anyway.  Don't assume that "many cases don't have a case fan," please -- and if yours is one of the many that don't instead of the many that do, spend the trivial amount of money and add one!  Cheap insurance against cooking a system.

Of course, if the power supply unit is what's cooking, that's the fan I'd check first.  99% of the time, a PSU fan is a standard 80mm or 90mm 5V fan.  It's perfectly replaceable.  If you feel uncomfortable opening up a power supply, sure, replace the unit -- it's more expensive, but it's still not breaking the bank or anything.
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slinkygn earned 250 total points
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Just saw your next comment.

If your PSU's fan spins, and still has sufficient torque (again, paper test or lightly try to stop it with your finger -- it shouldn't stop) -- you may also want to check that your PSU doesn't have two fans; many PSUs have a second fan on one of the internal faces to draw air in -- then, well, PSUs generate heat.  I imagine those are your favorite techs for a good reason; there's no substitute in cases like this for looking at something in person, and if they looked at it and cleared it, it would seem likely that you're good to go.
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by:smiffy13
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I'm wondering how good a job your techo's have done. When you look in the PSU grille does the fan and the components behind it look clean or do they look beige and dusty? Take the side off your case and see if the vents in the PSU are clogged with fluff and dust, if so then the fan won't efficiently draw air through the system. Your techo's should have blown all the dust out with compressed air, if all they've done is scrape the dust off the heat sink, it clearly wasn't enough.
If your case has space for a case fan, I'd certainly get one fitted if it was my system, but you need to work out why the PSU is getting so hot, it's a separate issue: putting a case fan in won't stop the PSU getting hot.  
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by:nobus
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it may also be the on-board fan speed sensor is bad - connect the case fan directly to the PS (with an adapter cable)
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by:rfs777
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Thanks for your help, it helped to have a clearer idea of the problem. The problem was the heat from the CPU fan near the PSU. We added an extra fan close to the CPU fan, changed the CPU fan settings (to be not so smart), and it all is a lot cooler now.
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