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Fan starts running super-high at startup?

Last response: in Components
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February 21, 2013 1:30:21 AM

Hey guys, I have a two year old HP s5-1110 Slimline computer that I transplanted into a full size atx case a few months back. Aside from running an extra fan and a different (new) power supply, the computer is stock and runs Win7. Never had a problem with it until tonight. The computer had been sitting for 10 hours or more (totally cold), pressed the power button, and one of the fans (I think the PSU fan) immediately started turning at a very abnormal super-high speed...Win 7 was booting up like normal, but I pulled the plug because I was afraid that damage would occur.

What would cause this? Thanks for any help you can give, I've got no ideas on this one.

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February 21, 2013 1:58:13 AM

I should add this; a month ago I had a dropped neutral in my house wiring that was causing brownouts....completely smoked the power supply in that computer. I replaced it and everything seemed to be fine; do you think there could be mobo damage from that? I would think I'd notice it right away...I've been using it for three weeks or so and it's been working fine.
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February 21, 2013 11:09:03 PM

I'm surprised no one took a crack at this. I started it up this morning, and it was like nothing ever happened. It's definitely not a thermal issue, so what else could it be?
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February 21, 2013 11:17:52 PM

Oh, this wasn't full speed, it sounded like someone took a 12v fan and applied 50v to it....I've never heard anything like that come from a computer fan before.
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a b ) Power supply
February 22, 2013 5:54:00 PM

You say the fan (not sure which fan?) started up at VERY high speed. How do you know? Is that based on very loud odd sound? MAYBE a fan is not running fast - it is making more noise than normal from bearings that are wearing out. This kind of thing is MORE likely to be noticed when a fan first starts up after being shut down and cold for a while, because that's when the fan bearings are loosest. After it runs for a short time the friction warms up the bearing and reduces the clearance in it, stopping the excess noise. (This is especially true of sleeve bearings.) If left unchanged, eventually the bearing will wear out more so that the noise does not stop. You should also be aware that, if this is what is happening, the fan actually is running SLOWER than normal and giving less cooling.

So, if that is your actual situation, get a replacement fan and install it before the current one stops itself completely.
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February 24, 2013 12:12:24 AM

Yeah, it's based on sound...it sounds like a vacuum cleaner when it's running fast. But I doubt it's a faulty fan; the PSU (including high-revving fan) is less than a month old...the rest of the fans are less than two years old.

I'm thinking that this is faulty fan control, and that something is intermittently overspeeding the fan at startup. But what? Is it a bios error? Mobo fault?

Oh, and bouncedk; no graphics card, this has integrated graphics.
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a b ) Power supply
February 24, 2013 12:41:51 AM

Control of the speed of the fan inside the PSU is almost always done within the PSU itself, and does not involve the mobo or its BIOS at all. Now, if what you observe is that this PSU fan runs VERY fast only for a few seconds (less than 15, say) at start-up, and then slows down substantially, that is exactly what it is supposed to do. MAYBE after that it runs so slowly and quietly you are used to that sound, and the start-up sound seems really excessive even if it is not.
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February 24, 2013 12:52:03 AM

Ok, that sounds logical except for one thing; it's intermittent. In every case the computer is cold on startup, so it's not a heat factor....sometimes it will run very fast at start (anywhere from 5 to 30 seconds or more) and sometimes it will not run fast at all. In order for the fast fan to be normal, would it not do it on every startup?
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a b ) Power supply
February 24, 2013 5:39:35 PM

Yes, although it might not be noticed always.

On a fan of this type the speed is controlled by varying the voltage supplied to it, from 0 to 12 VDC. The problem is that the fan cannot actually start with a very low voltage supplied. So the control system is programmed to start always at full 12 VDC to the fan, wait a short time (a few seconds) and then start to use its normal control process. This process compares the actual temperature measured with a sensor somewhere pertinent (in this case, inside the PSU) to a target value and changes the output voltage to get closer to the target. For a system that has not been running for a time and is cold, the action normally would be to slow the fan down a lot, or even to stop it. Later as the PSU heats up the fan will re-start if necessary or speed up. For a system that has been actually running recently, the action AFTER the initial few-seconds full speed will be to slow down a bit - how much depends on how warm the interior of the PSU is.

Given that, it is possible with a cold PSU that the initial full-speed start phase might last very few seconds before the control system reduces that to very slow or stopped. In some cases you might actually miss that brief fast burst.

This is not to say that a malfunction can't happen, or is not happening in your case. I just mean t is possible for you not to notice a normal start up that includes only a brief full-speed burst.
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February 24, 2013 5:52:44 PM

Interesting. I guess it's possible that I could miss the sound at startup, but because of how incredibly loud it is, it would have to be a really short burst for me not to notice.

But now I"m wondering; is it possible that the fan controller in the PSU might be flaky? The PSU is only a month old, but it's just a $20 ebay cheapie (brand name is Hurcules).

Thanks for your answers, I've already learned more than what I knew before.
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March 5, 2013 11:14:36 PM

Best answer selected by 9xer.
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