CPU fan failure - and more problems

HP Pavillion a230n
June 6, 2006 at 21:08:52
Specs: XP Home, 2.08 GHz AMD Athlon XP 28

Tonight my HP Pavillion a230n system shut down without warning. It rebooted itself and diplayed the message "CPU fan failure"

I opened it up and sure enough, when I powered it up the CPU fan didn't spin.

I had a 3 lead 12v spare of similar )slightly lower) current draw, so I plugged it in and it didn't spin either! To make along story stort, the original fan had a short so it was dead, but the replacement tested fine on the bench. When I measured the voltage on the fan power supply pin on the MB it read +8v instead of +12v and it dropped to 2.5 volts with the new fan attached. Sinec the new fan was rated foe a lower current draw than the old one it looks like the supply to the +12v pin has been hosed and it's supplying low voltage with very little current capacity. Not good.

For now I've attached a good 12v fan to the CPU and i'm powering it off one of the spare disk drive connectors. By hitting <F2> during boot I can overide the check on the fan speed so the system boots up and runs fine - it's just no longer monitoring fan speed.

It seems very odd that the voltage to the CPU fan seems low and has no current capacity, but everything else works fine. Am I missing something here? Should the system be adjusting the fan voltage based on the readout of the fan speed? Would the voltage read low if it wasn't getting a speed signal? I don't know how the speed monitoring circuit works. I guess it's possible the speed info output on the new fan is bad.

I'm thinking of maybe putting a 3 lead fan on the CPU, connecting the ground and 3rd lead (speed sensor?) to the old fan power supply connector and connecting the +12v to one of the drive connectors. Any way this could be a problem? If there is something wrong on the motherboard, I'm not inclined to dig around and try to find it.

I suppose I can always just hit <F2> on boot and run the fan unmonitored, though next time it fails I wonder if the CPU will meltdown!

Any comments greatly appreciated.


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#1
June 6, 2006 at 22:20:35

i had a similar problem with an aerocool fan. it seems that the draw from the mobo was alot more then it should have been and ended up blowing a capacitor. therefore rendering my cpufan plug useless. later more caps blew and i found out it was due to a faulty PSU. i dunno, just be weary. you never know.

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#2
June 6, 2006 at 22:36:33

In order for the system to monitor the FAN speed, your fan must have a 3-pin connector connected into the motherboard (it should say CPU-fan on the 3-pin connector located near the heatsink)... The red wire is +5-12v depending on supplier, black wire is ground and yellow wire is RPM detector. If you bought a fan with only 2 connector like red wire + black wire, then you will not see the fan RPM in the BIOS.. If you connect the FAN to the 12v rails like 3-pin to 4-pin converter that connect to hard drive, cd rom... etc You will not get the RPM since it only provide the voltage but not RPM detector...


TMP-Man

Asus P5P800-SE
P4 506 @ 4100Mhz 1.525v
Thermaltake CLP0024 w/ 2000RPM FAN + AS5
1GB Corsair 2-3-3-5 DDR400
40GB 5400RPM/120GB 7200RPM HD
Radoen 9500 mod 9700 @ 375/600 CHS+RHS


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#3
June 7, 2006 at 08:17:34

The mobo has the three pin, so my thoughts were to use a spare drive connector to provide the power, but to get a 3 lead fan and connect the speed sensor lead to the speed sensor pin on the mobo connector (the fan I'm using now is only two lead).

I don't know exactly what signal the third lead provides. I'm guessing maybe a series of pulses, one per fan rotation?

If it does and the mobo 3 pin and drive connectors share the same ground, I'm hoping that the fan speed will be sensed OK and I don't need to use the mobo connector to provide power.

Otherwise I guess I could shut off the fan speed sensor via the BIOS and just keep my fingers crossed that it never fails!


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