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Old 10-26-2011, 08:04 PM
daquigle daquigle is offline
 
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Default CPU Fan constantly revving up and down

I have a desktop computer that revs the fan up whenever anything is happening on screen, including simply moving the mouse. If it's sitting idle the fan spins at the normal rate, but any activity and it sounds like it's getting ready for takeoff.

First thought was overheating. The CPU (dual core) temps were reading a steady low to mid 30's C, but I went ahead and cleaned the heatsink and processor and reapplied the thermal paste. Started it up again and it's no different, though the temperatures are reading slightly lower than before. This is with speedfan.

Most recently before I last gave up on it I checked the bios and the temps there on one of the cores was bouncing all over the place. From 250F to negative readings. The machine never has never shut off like I would expect from overheating, and runs normal within Windows, just with the fan revving up and down all the time.

Now I'm thinking the temperature sensor is failing to get the proper readings. If that is the case I've never experienced that before, but I would expect speedfan is using those same sensors from within Windows and it's showing normal readings. So basically I'm at a loss as to what the problem is. It's a clean install of Vista on a new hard drive within the past two months. The problem showed up in the past week. Nothing extra appeared to be running in the background but I checked it out for any malware just for due diligence and it is clean.

I haven't found anything through Google that is a similar situation to this so I thought I'd check here. If you have any ideas it'd be appreciated. This is a bench machine so it's not a high priority for me, just quite the sound nuisance.
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Old 10-26-2011, 08:59 PM
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Question. Is there a setting in bios that enables you to disable " automatic" fan mode and to set a static speed. Then monitor the temps to see that it isn't overheating. Just a thought, don't know if this is practical or not. Regards


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Old 10-26-2011, 09:41 PM
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have you hooked up another fan to see if it is still doing it? Possible fan problem?
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Old 10-26-2011, 11:34 PM
ray90813 ray90813 is offline
 
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You sure its not a dynamic feature of the motherboard that automatically adjusts fan speed according to load and temp.

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Old 10-27-2011, 02:53 AM
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Its either the fan or motherboard.

hook the fan up to another motherboard or power source and see how it runs, if it runs good, might need a replacement motherboard.
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Old 10-27-2011, 03:20 AM
daquigle daquigle is offline
 
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Quote:
Originally Posted by bertie40 View Post
Question. Is there a setting in bios that enables you to disable " automatic" fan mode and to set a static speed. Then monitor the temps to see that it isn't overheating. Just a thought, don't know if this is practical or not. Regards
That setting is there and I had already tried running with it disabled. When I did that it just ran the fan super fast all the time. There was no bios setting to control the fan speed even with the smart control disabled. Temps looked good either way though.



I'll try a different fan and see what that does. If it's a motherboard problem it's more than likely not going to be worth replacing. Thanks for the input!
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Old 10-27-2011, 07:49 AM
RegEdit RegEdit is offline
 
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What is the temperature of the CPU?
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Old 10-27-2011, 01:02 PM
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Quote:
Originally Posted by daquigle View Post

Most recently before I last gave up on it I checked the bios and the temps there on one of the cores was bouncing all over the place. From 250F to negative readings. The machine never has never shut off like I would expect from overheating, and runs normal within Windows, just with the fan revving up and down all the time.
You definitely have a sick mobo on your hands.
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Old 10-27-2011, 02:13 PM
jbartlett323 jbartlett323 is offline
 
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I would recommend forgetting what windows says about temps, especially if bios is giving you strange read-outs. Windows temp readers are notorious for being incorrect. They are always between 1-7 degrees off no matter what, and if things aren't working right, it will be much, much worse.

First i would set that fan to full go, AKA disable dynamic fan speed. Its all but useless anyway, aside from acoustically, and can cause procs to overheat from never actually getting to 100% rotation. It may be loud, but at least you know without a shadow of a doubt you are getting needed cooling.

Next i would check for a BIOS update. most times issue like this present themselves immediately, but sometime it takes awhile and there was a flash fix the whole time.

Also, get an external temp gauge. Just a cheap laser pointer type works great. Measure the temp on the side of the heatsink. It should be ~5-10 cooler than the proc is reporting. don't test through the fan though, you will get really low temps and a inacurate reading. While your there, measure temps for RAM, NorthBridge, and SouthBridge. Some boards will kick the fan up for Northbridge also, as the stock cooler is designed to push air over it also.

If all temps pass, and the BIOS does nothing for you: Replace the Proc, not the board. The temp sensor is on the proc, is read from the proc, and has nothing to do with the board in most cases. If its the Northbridge causing the issue, you'll know with the temp readings....
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Old 10-27-2011, 03:46 PM
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Quote:
Originally Posted by jbartlett323 View Post
The temp sensor is on the proc, is read from the proc, and has nothing to do with the board in most cases.
I have had a MB with a failing transistor that was involved in sensing CPU temp and fan control. A colleague who does MB repairs spotted it and fixed it. So it could still be the MB, but you did say "in most cases."
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