[SOLVED] old PC's new chassis fan running at 100%

voodoogiant

Distinguished
Jan 6, 2008
3
0
18,510
I noticed my wife's old PC built in 2011 is extremely dusty inside so I replaced the old chassis fan with a new Corsair ML120 PRO fan I've used in my computer. It has a 4-pin connection, but it plugged it into a 3-pin input on the old M3A770DE motherboard replacing the 120mm fan that came with the case (also a 3-pin).

The fan is blowing tons of air out, but it's obviously going at 100% all the time. Much louder than it was before. It doesn't sound like a mechanical problem. Just working at 100%.

I went into the BIOS and see the fan speed isn't reported like the CPU and power supply are and don't see any other controls for slowing it down.

Any advice on slowing this fan down? Did I install it incorrectly?
 
Solution
Actually, the item cited above has it backwards. If you plug a 3-pin fan into a header using PWM Mode, it will always run full speed. Of you plug a 4-pin fan into an older 3-pin header, its speed WILL be controlled.This is a backwards-compatibility feature of 4-pin PWM fan design. So that's not your issue, OP.
Actually the article is correct.
You can control 3pin fan in 4pin fan socket, if BIOS allows change of fan control mode from PWM to linear voltage.
You can not control 4pin fan in 3pin fan socket. It either runs at full speed or half speed all the time.

Paperdoc

Polypheme
Ambassador
Actually, the item cited above has it backwards. If you plug a 3-pin fan into a header using PWM Mode, it will always run full speed. Of you plug a 4-pin fan into an older 3-pin header, its speed WILL be controlled.This is a backwards-compatibility feature of 4-pin PWM fan design. So that's not your issue, OP.

I am sure the root of this is as you suspect: that mobo never had any means to control the speed of its chassis fan. We should assume the only thing that header does is supply fixed 12 VDC power so the case fan can run full speed all the time. The manual's notes basically say that ONLY the CPU_FAN header can control its fan's speed if you let it, and even then ONLY using the new 4-pin PWM Mode. It does NOT have any option for controlling a 3-pin cooler for the CPU.

You can get a manual controller for this that fits into an unused PCI slot opening on the back of your computer

https://www.amazon.com/Yuhoo-Practi...omputer+fan+speed+control,aps,75&sr=8-64&th=1

Note that, on this page, ONLY the "Type 2" model is shipped from Amazon in the USA - the other models are shipped from China. This Type 2 model simply inserts a variable resistor into the fixed 12 VDC power supply. It plugs into your mobo CHA_FAN header, and then you plug you fan into it. Other models of this (and other sellers) may offer more outputs to supply several fans from one control knob, but they draw power directly from the PSU via a connection to either a SATA or a Molex PSU output. There also are simple devices that look like little circuit boards with a small sliding switch, and they offer three speed choices only: Off, Low, High, and usually get power from the PSU.
 
Actually, the item cited above has it backwards. If you plug a 3-pin fan into a header using PWM Mode, it will always run full speed. Of you plug a 4-pin fan into an older 3-pin header, its speed WILL be controlled.This is a backwards-compatibility feature of 4-pin PWM fan design. So that's not your issue, OP.
Actually the article is correct.
You can control 3pin fan in 4pin fan socket, if BIOS allows change of fan control mode from PWM to linear voltage.
You can not control 4pin fan in 3pin fan socket. It either runs at full speed or half speed all the time.
 
Solution

Paperdoc

Polypheme
Ambassador
Of course you can control the speed of a 3-pin fan by a 4-pin mobo header IF the header configuration allows you to change it to behave exactly as a 3-pin header. Then it is no longer a "4-pin header"!

The design of 4-pin PWM fans included the backwards compatibility feature I cited (CAN control its speed from a 3-pin header). In large part that was to ease the introduction of the new design to the marketplace that, at the time, had ALL mobos built with ONLY 3-pin Voltage Control Mode headers. You should try it. Might be difficult with today's mobos becasue almost all now have 4-pin headers, and MOST (but not all) CAN be changed in their configuration screens. But try the fan outside a computer, with some wires and an assortment of batteries. Remember that the female connector pinout is that Ground in Pin 1, and +VDC supply is Pin 2. Try connecting to the fan Voltages of 12 VDC, 9VDC, 6VDC. I bet you will find the speed IS different (not just either full or half speed) when you supply those voltages with NO PWM signal supplied on Pin 4.