# Broken CPU temp sensor causing high fan activity

## Lunar_Lamp

The temp sensor for my CPU is broken I think.  If I leave the machine off for hours, turn it back on again, go straight into the CMOS setup screen and view temperature of the CPU, it is 127celcius.  lm_sensors gives a similar reading during operation, but the CPU shows no negative effects of this, and will quite happily perform long emerges and other processor intensive tasks.  

Now, this in itself is not an issue, what is an issue is that it causes the fans in my box to run as they are trying to make the machine lift-off.  Being a small form factor machine (MSI Mega 180) these small fans are not the nicest sound to the ear either.  I don't want to just remove them obviously, but I can't think of a software/hardware hack that can solve this problem.  I'm sure a software hack is possible as the fans are not set to lift-off mode until after the grub screen - i.e. they seem to be software controlled at some level.  However, I've no idea where to go about sorting this out - acpi seems a likely starting place, but an area I've not investigated too much.

Any tips would be much appreciated, and if you would like more info (e.g. hardware specifics) etc, please feel free to ask.

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## coolsnowmen

If this is a desktop with out a way to control the fan speed in software, I'll hardware the fan to medium if you were in a non-hazerdous (low external heat, good circulation)

Is this a three of four wire fan?

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## Lunar_Lamp

This is a 3wire fan, but I'm not really sure how to lower the speed of the fan via a hardware mod.  I was sure there'd be a software method - even if it was to link the speed of the fan to the load of the CPU rather than the temp of the CPU temperature sensor.

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## coolsnowmen

if a way to control the fan exists it is _probably_ through lm_sensors.  It is worth going through it if you havn't before. But You should probably get the newest kernel, as sensors are added to the kernel with every revision, and then go through a lm_sensors howto, 

the lm_sensors package in gentoo, contain a program called fancontrol

I've never used it but it looks like something that could help you.

```
SYNOPSIS

       fancontrol [configfile]

DESCRIPTION

       fancontrol  is  a shell script for use with lm_sensors. It reads its configuration from a file, then

       calculates fan speeds from temperatures and sets the corresponding PWM outputs to the computed  val-

       ues.

WARNING

       Please  be careful when using the fan control features of your mainboard, in addition to the risk of

       burning your CPU, at higher temperatures there will be a higher wearout of your other hardware  com-

       ponents, too. So if you plan to use these components in 50 years, maybe you shouldn't use fancontrol

       at all.  Also please keep in mind most fans aren't designed to be powered by a PWMed voltage.

       In practice it doesn't seem to be a major issue, the fans will get slightly warmer, just be sure  to

       have  a  temperature  alarm and/or shutdown call, in case some fan fails, because you probably won't

       hear it anymore ;)

```

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## Lunar_Lamp

To generate the fancontrol config file I needed to run pwmconfig.  It tells me that there are no  pwm-capable sensor modules installed.  Looks like I'm going to have to stick with this really loud fans unless anyone can think of any other way around it?

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## coolsnowmen

only because you didn't give much information...

you followed a guide similar to this right?

http://gentoo-wiki.com/HARDWARE_Sensors

I only ask because some of those config programs can only see modules you have built/inserted, so for good measure I remember building a whole bunch of them just to find the 4 or so I really needed....

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## bunder

if you haven't yet, you can always try fixing your dsdt, or if all else fails, buy a new motherboard (and/or cpu fan, depending on where the sensor is)

cheers

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## Lunar_Lamp

I looked into fixing dsdt, but there is only one warning to fix, and I'm not sure that it would sort me out as BIOS seems to be reading the temperature as 127celcius also.

I've already configured lm_sensors etc, and it just appears that there is no way for me to control the fans from there using pwm.   Perhaps there are other ways though.

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## Wojtek_

I had exactly the same problem (mine reached only 105C though). I've called Fujitsu Siemens and they replaced my cpu and motherboard without any hesitation.

Cheers,

Wojtek

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## Lunar_Lamp

Unfortunately this is a reasonably old barebones system that I am certain will be out of warranty.

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