fan speed issue

[iballew]

So recently I bought and installed a msi 760gm-p21 motherboard into an old case I had and ever since I first booted the thing up, the cpu fan has been running at full blast without any rpm variation. I installed windows 7 without any issues and made sure the bios was up to date. I have played around with the bios settings and tried setting them to default but nothing has worked. The cpu is running at 33 degrees Celsius so there is no reason it should be doing this. Thanks in advance for the help.

 

[Darkbreeze]

First off, go back into bios and select "optimal settings". Then go into H/W manager in the BIOS and there should be options for the fan controls. It may be that you have your CPU fan connected to the wrong header on the motherboard. Make sure it's connected to the header that says CPU fan and not the one that says sys fan. Also, in control panel power options, you might see what plan it's set on and change it to balanced if it's set on performance.

 

[iballew]

I have fixed the problem. The heatsink I borrowed off of an older machine only had three prong holes (whatever you call it) and the board had a four prong connector. It fit like it was suppose to and I assumed the fourth prong was not necessary. Well I became suspicious of this prong and looked up what it was suppose to do. It was labeled as fan control. After that, I looked for a fan with four prong holes, slapped it on the heatsink and poof!!! It worked like a charm. I suppose this motherboard controls the fans more precisely so it needs that extra prong. Thanks for the thoughts and the quick reply.

 

[Darkbreeze]

As I said, you needed to be connected to the 4 PIN CPU header. Using the 3 pin system fan (Case fan) header would not work properly nor would using a three pin connector on a 4 pin pulse width modulation CPU header. It will get power but the power would not be controllable using PWM since the 3 pin can be controlled only using voltage regulation and is not supported on the 4 pin header. Glad you got it worked out though. In the future and for any future builds, keep in mind that PWM or Pulse width modulation is the better option for controlling fans precisely.

It doesn't require changing the amount of voltage to control fan speed as some fan headers, especially on older systems, are designed for. It keeps voltage steady but rapidly turns the voltage on and off at a specified duty cycle to increase or decrease speed. If you have a board capable of controlling using PWM that's probably what you want to use in almost all cases. This also applies to case fans, not just CPU coolers. There are a lot of aging cases that have 4 pin Molex (Like the IDE power connectors that connect to older CD and DVD drives) connectors delivering power to fans which only allows for full speed operation too. It's definitely not very efficient and if you have a three pin or a four pin motherboard connector, you generally want to use a fan that has a similar connector.

 

[iballew]

The thing that got me was the older system could control the fan using the three pin voltage system, so why couldn't the four pin? Now I understand they are two completely different ways of controlling fan speed! That is nice to know for future builds/tinkering. I do have one more question. I hooked up a case fan this morning and it just wants to run at half speed (2500 rpm or so) which is too loud for my taste. Unfortunately, the motherboard uses the three pin header for the case fan. Does this mean I cannot change the fan speed at all? The case fan is fairly small. Is it giving voltage that is meant for a larger fan that uses more power?

 

[Darkbreeze]

What size is the case fan, and is there only one? The three pin sys fan header should be able to control voltage. This setting should be under H/W monitor in the BIOS as well. What is your case model?