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Problem with noisy fan

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whiz115

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Hi!

recently i changed the 6 month old motherboard for my PC with a new one.. and i'm facing problems with the CPU fan because electric noise passes from the motherboard to the fan and it's very loud!!! with the previous motherboard everything were fine.

i can't stand it because every time i'm running a program or move the mouse the noise changes! if i disconnect the fun goes away.

any help?
 
yes... and i'm having the noises after the change of the motherboard.

i'm sure it's electrical noise...though i'm going to do one last test...i'll connect the fan with a 12V psu so i can be 10000% sure. :rolleyes:
 
the fan works just fine without noises with an external psu...i also tried few capacitors i had in front of me and still nothing the noise remains... (1uF, 47uF, 100nF,270pF)
 
PhillDubya here you are a photo says it all.

guys any help? i can't work on my computer like this! :rolleyes:
 

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some reasons:
1.fan motor gets electrical noise and works as a speaker.
2.incompatible fan produce noise and heard in the smal cpu speaker.
 
some reasons:
1.fan motor gets electrical noise and works as a speaker.

that's the case!

and when i'm disconnecting the PWM control pin the noise totaly stops!
although the fan works at full speed.

@blueroomelectronics can you help? you can't imagine how noisy and annoying is! the "Intel quiet system" logo in my case looks ironic!
 
Turn off the PWM fan control and see if the problem goes away. You need both the resistor & cap for the fan mod to work at all (it's an integrator)
 
as i said if i remove the PWM control wire from the socket then the noise goes totaly away, but the fun works at full speed.
 
You could buy a fanless powersupply if the noise bothers you. Or a large fan type supply they tend to run slower.
Of course you could try the PWM mod in the app note.
 
You could buy a fanless powersupply if the noise bothers you.

it's the CPU fan!!!!!!! :D

the 4 pin type...

P1 Black Ground
P2 Yellow +12 V
P3 Green Speed sensor wire (RPM)
P4 Blue PWM (Pulse-width modulation) control wire


Of course you could try the PWM mod in the app note.

do you think it worths spending time on it? as i said i already tried
few capacitors from +12V to GND and did nothing! but that was before i discover the pdf link i gave you!

thanks bill.
 
I believe he is strictly talking about the PWM CPU fan.


@Whiz: Is your sound card's speaker connected to another socket on the computer's case? Like an external socket for attaching headphones?

The noise you are hearing, are you using headphones, or just external pc speakers?
 
Hi,

Yes, you need a capacitor but also a series resistor.
The cap goes in parallel to the fan, and the resistor goes in series
with the capacitor from the PWM control signal.
You might try different value resistors like 1k, 2k, 5k, etc.,
and 1uf, 10uf caps.

The idea is to stop the pulsing from getting to the fan motor and
supply it with a smoother voltage instead. The resistor and cap
do this, but the cap alone wont work as well.
 
i don't need headphones to hear the noise!!!!

and also it's not a solution to disable the PWM control wire so i can
totaly stop the electrical noise.

[edit]

@MrAl do you think it will work? not all motherboard have the same fan control IC.
the PDF link i gave is a random one i got while i was searching the net.

also Analog Devices produces such ICs...
ADI - Analog Dialogue | Fan Speed Control


btw why is that happening??? i guess it's not normal? defected motherboard? if i don't find
a solution with the fan should i RMA the motherboard?
 
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