CPU Fan will not turn on

[munkydotorg]

My CPU fan will not turn on. I thought my old one died so I replaced it with a newer Thermaltake unit.

It will occassionally make a short spin, but that is it. My system will turn on then turn off once it hits thermal shutdown.

I have changed the settings in BIOS from SMART controlled to Always On. Nothing changed.

I'm running a 2.8Ghz P4 (800MHz FSB) on a Biostar P4TSV m/b.

If anyone has any suggestions, I'm all ears.

[Hagar]

Try another FAN connector on the motherboard.
Or get an adapter to power it from a 4-pin Molex connector (harddisk power).
Or get one of those fan controllers that acts as a fancy adapter.

These suggestions base on the theory that your CPU_FAN connector on the motherboard is bad. It is using a transistor to regulate the current (PWM), this transistor can fail.

[Rick]

Does your fan connector ( On the Mother Board) have the 3 or the 4 pin connector ?
If it is 4 pin and the new fan has only 3 then you have no smart fan.
Make sure you have the fan connected to the correct pins.
By the small tab on the connector it should line up with the slot in the connector

All these bing correct and the fan not working but the system still booting
Tells me you may have a case fan connected to the CPU connector

Boot up and go into the bios
Find and check the health or system monitor
Look for the cpu temp and fan monitor
See what it lists for fan speeds
IF the fan speed is set to ignore
DON'T change it right away .. You need to get a fan on the connecotr and spinning before you enable it
Other wise the system will not detect a fan spinning and will shut down at or shortly after bootup

IF You install a Molex connector ( 4 pin ) http://en.wikipedia.org/wiki/Image:Molex_female_connector.jpg to fan adapter Make sure you have the Yellow wire from the fan connected to the CPU connector on the mother board
Like this one
http://us.st11.yimg.com/us.st.yimg.com/I/sidewindercomputers_1961_5131989
Otherwise the mother board will not read any fan spin and cause a system shut down

[Whyzman]

Rick turned me on to the molex RPM sensing adapters long time ago. I use them on all builds to keep the 12V fan power supply off the motherboard headers, yet provide necessary RPM sensing to the motherboard.

Amost all newer motherboards are designed to protect the CPUs by shutting down if RPMs are not sensed.

If you are actually powering on and shutting down due to thermal issues it sounds as though something more sinister may be at work. Usually, a lack of CPU RPMs will not allow you to proceed with the boot process, shut down is immediate.

However, if you have a case fan with an RPM sensing lead on it plugged errantly into the CPU fan header...the motherboard is not capable of distinguising which fan it is monitoring. It would boot up thinking the CPU was being cooled and shut down due to overheating...

[Fruss Tray Ted]

Could be fan sensor, the power good sensor for the mobo or the PSU. These would be the areas to look at IMO. But one more possible problem would be if you had a faulty component connected to the motherboard and it is interfering with the boot process. Do a barebones boot to eliminate that possibility.