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Mark PoirierFlag for Canada

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Curious about a Dell Dimension 4600 cooling fan with thermistor-->pulsing on and off

I have a Dell dimension 4600 desktop on the bench with a JMC-Datech 9232-12hb cooling fan which is attached to the case and draws air through the heatsink by way of a cowling over the heatsink. It has a thermistor set up on the stationary hub of the fan housing which monitors the air temp, and adjusts the fan speed accordingly.
The problem is the fan is running fne until the computer is stressed. While using a burnin test, the fan begins to ramp up in speed and then when it reaches high rpm's it shuts down then ramps up over and over again. Sounds just like a heavy breather over the phone.
I have already changed out the fan and now have a working cooling system.
My question is--> has anybody out there ever seen this type of behaviour in a thermistor controlled fan , and could it be indicative of any other hardware failure on the motherboard itself?
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eudmian

I had a similar issue with a  Sony Vaio system.  I decided for various reasons to wipe the drive and reinstall the OS (WinXP Pro) and that is when it started.  Exactly as you described it would ramp up on load and then cycle, VERY annoying on a system that sat on my desk next to me.  

I never did have the time nor inclination to delve further into it but found it interesting that it was an OS patch that remedied the problem in my case.  The fan and sensors are directly controlled by the BIOS with the OS being able to monitor and in some cases pass commands to them so from a hardware standpoint short of a faulty BIOS, which is easy to check, I cant think of anything else that may be contributory.

I might reccomend, if you have not already, run a load test from a live CD like Knoppix.
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ASKER

Thanks for the input.
Did your fan have the thermistor on the fan body( looks like a green nub sticking out of the fan hub) or was the fan speed dependent on  hardware sensor readings from the motherboard?
I have burnin running to stress the cpu making it heat up and the NEW fan is ramping up slowly and not pulsing on and off anymore. There are no  bios settings concerning  temp controls (DELL makes em' lean) so I guess the thermistor is the only control involved. Can't even find a sensor with speedfan to check a temp with.

Concerning that patch, was it specific to the viao or was it an XP patch?
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eudmian

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