Help me diagnose a cpu fan

[daytonl]

I have a boxed Celeron 266 on an Abit bx6 r2 motherboard. The cpu is brand new and for some reason the Fan does not run. I don't have another fan to test the header on the motherboard. I did get a voltage reading of 5.10V on the green wire, 1.13V on the yellow wire and 0.9V on Black. Looking at the 5V base voltage I am assuming the motherboard is not the problem. I also tried 2 different headers for the fan and neither made a difference. How can I be sure its the fan and not the motherboard? What resistance values should I look for on the fan? Any other help is greatly appreciated, I need to get this fixed as soon as possible.

Thanks

 

[Viperoni]

Check the voltage across the black and red leads.
Those are your fan power leads, the green one if the RPM lead.
BTW: 5v isn't enough to run the fan, you really should be pushing 12v.

 

[kaitain]

I thought CPU fans ran at 5V - the chunkier case fans run @ 12V. Try running the fan from a battery. Well away from the computer, shove a paperclip into each pin-socket, and try to run the fan from a 9V (small square) battery. If it doesn't work either way round, you might have a dead fan...

 

[daytonl]

Well I did a little more testing. I jumpered the cpu fan directly to the power supply instead of the fan header. The fan worked immediately. Some of the original information I wrote was wrong. The cpu fan has 3 wires. Green, Yellow and Black. Yellow is power, Black ground, and I guess Green is rpm as Viperoni said.

I checked voltage at the header with no load and I got the following voltages
Yellow = 12.25V
Green = 5.09V
Black = ground

12Volts is enough to run the fan so I had to check Voltages under Load. They are:

Yellow = 2.97V
Green = 0.43V

Obviously 3 Volts isn't going to be enough to run the fan. I don't know why I'm getting these huge drops under load. I guess the motherboard is at fault. If someone can give me a reason for this problem it would help a great deal. I bought this motherboard used off someone on E bay its really discouraging to have this happen. I will have to get in contract with the seller.

Thanks for your help