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I have a motherboard for a HP business desktop dx5150 PC. The model written on the board is "MS-7050" and it is for an AMD socket 939 processor. I got everything installed in it, and when I turned it on, it showed a message stating that there was a "CPU Fan Error" (or some similar language) and then turned off. It never stays on for more than about 30 seconds, probably less.

The fan had previously been working great, but I replaced it anyway with a brand new Cooler Master fan. This did not work. I then reset the BIOS with the jumpers on the board, no dice. I replaced the CMOS battery. Same error. I then replaced the entire computer power supply with a brand new Antec, same error.

The fan header is keyed, and has room for 3 pins. The CPU fan is designed the same way, so its not that I'm missing a temperature sensor or anything.

Can anyone give some suggestions? Especially maybe some secret keystrokes to bypass this error?

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5 Answers

I've had the very same problem -- a perfectly working cpu fan which when on automatic control comes to a halt, and so the motherboard prints that the cpu fan has failed and switches off.

The fan and motherboard are both working fine, and the cpu is not overheating (you can leave it on the BIOS "health" screen for ages and the cpu temperature doesn't get above about 45C).

Unfortunately if you disable the fan control (and power-off on fan fail) in the bios then the case fan I have is incredibly loud (since it's at full speed), so I had to combine this with a separate fan controller for the system/case fan. These two combined solve this problem for me, but the main problem seems to be that the cpu fan control by the motherboard is a bit too aggressive at slowing it down, and I guess that some fans stop rather than running fast enough for the fan check to be happy.

It may be possible (although I haven't tried) to disable the motherboard fan control so they run at full speed, and then to slow down the fans once you've booted an OS using something like SpeedFan (on windows).

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I had this problem recently and solved it by doing the following.

  • Press F10 on bootup to enter the BIOS
  • Select "PC Health Status"
  • Set "System Fan Fail Check" to Disabled
  • Set "Fan Control" to Disabled
  • Save the settings and reboot
  • Use your favorite utility to check your CPU temperature to ensure that your CPU is cool enough.
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From the HP Service Manual:

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00307105/c00307105.pdf

Warning: CPU fan has failed. CPU fan weak (RPM < 1000) or not turning. Ensure that the CPU fan power cable is connected. If the problem persists, replace the fan.

Warning: System Fan has failed. System fan weak (RPM < 1000) or not turning. Ensure that the System fan power cable is connected. If the problem persists, replace the fan.

Look at the front panel when the unit is on, does it exhibit the following:

Red Power LED flashes two times, once every second, followed by a two-second pause. The Power LED will continue flashing until the problem is resolved. (Pertains to CPU fan only)

Processor thermal protection activated: A fan may be blocked or not turning. OR The heatsink/fan assembly is not properly attached to the processor.

  1. Ensure that the computer air vents are not blocked and the processor cooling fan is running. Leave a 4-inch (10.2-cm) clearance at the back of the system unit and above the monitor to permit the required airflow.

  2. Open hood, press power button, and see if the processor fan spins. If the processor fan is not spinning, make sure the fan's cable is plugged onto the system board header. Ensure the fan is fully/properly seated or installed.

  3. If fan is plugged in and seated properly, but is not spinning, then replace processor fan.

  4. Reseat processor heatsink and verify that the fan assembly is properly attached.

Could be a bad fan out of the box or a defective motherboard fan controller as others have said.

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+1 because you found the actual service manual and quoted relevant information directly from it. Well done! –  Randolf Richardson Jun 19 '11 at 15:12
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It never stays on for more than about 30 seconds, probably less

To me this indicates that the CPU is overheating. It's possible that "CPU FAN ERROR" is just a generic message that the CPU isn't being cooled properly. Check that the heatsink is properly installed. If you've got it lying around, throw on some thermal grease.

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Ah, of course (+1), this is most likely the correct answer! –  Randolf Richardson Jun 19 '11 at 3:16
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Assuming the CPU fan is plugged into the motherboard correctly, I would assume that something with its electronics (which communicate with the motherboard to indicate fan speed, etc.) are defective and contact the vendor to arrange for a warranty replacement.

If you can plug that fan into a different motherboard, and it works okay there, then you may have a defective motherboard on your hands, but I suspect it's most likely the fan.

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+1 Actually, I think yours is the right answer. I think the MB was proably damaged from heat as the previous fan went. He said in his question "I got everything installed in it, and when I turned it on, it showed a message...", which would indicate it was cold when turned on (or cold at some point, and he would have mentioned it happening then), so the CPU cannot have overheated yet. –  KCotreau Jun 19 '11 at 3:29
    
A point of clarification (I'll edit above with details) is that this motherboard is a replacement for a previous motherboard. So, the MB cannot have been damaged by heat- it has never been fully turned on in my system. –  John Jun 19 '11 at 5:06
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