|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.