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CPU Fan error

Last response: in Components
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February 21, 2010 1:01:12 PM

I have the same problem. This happened after I changed the battery. "CPU fan failed", but it is running. Also it tells me to hit F2 to enter the bios but I cannot it shuts down before the setup starts.

More about : cpu fan error

a b ) Power supply
a b à CPUs
February 22, 2010 12:22:58 PM

Oh, that's a nasty Catch-22! Many modern mobo's monitor the CPU fan speed to be sure it is working. If it fails entirely - that is, its speed signal drops to nothing - the BIOS will shut down the system immediately without waiting for the CPU to overheat. This is a protection measure. But to get it to work, obviously, you must be using a CPU fan connected to the mobo CPU_FAN pinout. If you are not, there is a spot in the BIOS control of CPU Fan speed that allows you to disable this protection. However, in your case it appears it will not run long enough for you to enter BIOS and change the setting!

This all happened when you changed the mobo battery. That probably made the BIOS do a Factory Default reset of its settings. Maybe that is how this got changed. Is your CPU fan connected to the CPU_FAN pinout on the mobo? And, is it a 3- or 4-pin connector with 3 or 4 wirse from the pinout to the fan? If is IS that way, re-check the fan connection. Unplug and reconnect it a couple of times in case it just got loose and is failing to feed the speed signal back to the mobo. If it is NOT, and your CPU fan is powered and connected elsewhere, then I suspect the default reset put that alarm circuit back into operation and it's being triggered by lack of speed signal.

In either case, if it still does not work MAYBE you can get things going again by fooling the mobo. First, make sure your CPU fan is powered at all times so it is cooling the CPU. If necessary, plug it in someplace else or rig a temporary connection to its two fan power leads (on 3-pin fan, this is the black and red wires). Then borrow a real 3-pin fan and plug that into the CPU_FAN mobo connector and turn on the system. This just may provide a fan speed signal to the BIOS so it does not shut down. Go immediately into BIOS and do two things. First, go to the area where you can load a set of BIOS settings and Load the Optimized Default settings. Then go to where the CPU fan is controlled and look for where you can shut off the CPU FAN speed emergency shut-down system. Save and Exit. After booting, shut down and reconnect your fans normally, then reboot.

If all this works, you may have one more step. As I said, this whole sequence has resulted in resetting all your BIOS settings to some default set. If you had any custom settings, you'll have to go back into BIOS and reset them the way you want.
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February 23, 2010 2:25:10 PM

Paperdoc said:
Oh, that's a nasty Catch-22! Many modern mobo's monitor the CPU fan speed to be sure it is working. If it fails entirely - that is, its speed signal drops to nothing - the BIOS will shut down the system immediately without waiting for the CPU to overheat. This is a protection measure. But to get it to work, obviously, you must be using a CPU fan connected to the mobo CPU_FAN pinout. If you are not, there is a spot in the BIOS control of CPU Fan speed that allows you to disable this protection. However, in your case it appears it will not run long enough for you to enter BIOS and change the setting!

This all happened when you changed the mobo battery. That probably made the BIOS do a Factory Default reset of its settings. Maybe that is how this got changed. Is your CPU fan connected to the CPU_FAN pinout on the mobo? And, is it a 3- or 4-pin connector with 3 or 4 wirse from the pinout to the fan? If is IS that way, re-check the fan connection. Unplug and reconnect it a couple of times in case it just got loose and is failing to feed the speed signal back to the mobo. If it is NOT, and your CPU fan is powered and connected elsewhere, then I suspect the default reset put that alarm circuit back into operation and it's being triggered by lack of speed signal.

In either case, if it still does not work MAYBE you can get things going again by fooling the mobo. First, make sure your CPU fan is powered at all times so it is cooling the CPU. If necessary, plug it in someplace else or rig a temporary connection to its two fan power leads (on 3-pin fan, this is the black and red wires). Then borrow a real 3-pin fan and plug that into the CPU_FAN mobo connector and turn on the system. This just may provide a fan speed signal to the BIOS so it does not shut down. Go immediately into BIOS and do two things. First, go to the area where you can load a set of BIOS settings and Load the Optimized Default settings. Then go to where the CPU fan is controlled and look for where you can shut off the CPU FAN speed emergency shut-down system. Save and Exit. After booting, shut down and reconnect your fans normally, then reboot.

If all this works, you may have one more step. As I said, this whole sequence has resulted in resetting all your BIOS settings to some default set. If you had any custom settings, you'll have to go back into BIOS and reset them the way you want.



Thanks for the quick response. I'll give it a try and let you know.
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