CPU Fan not detected???

[DoDicK]

Hi All,

I bought a new Cpu fan which is more powerful and thicker than the one that is currently connected on. I followed the correct polarity for the new Fan to work. The fan did run but the m/b can't detect it. I think the problem is that the new fan has only 2 wires while the old/currently connected has 3 wires. Hmm???

BTW, I bought the fan on electronic shop.

Same thing happens on my new Chassis Fan. Pls help...

Thanks,
/dDk

Duron 700mhz@700mhz
128mb-Pc133 SDRamm
20GbMaxtor
Savage 3d

[soniclos]

Yes your old fan had a Tachometer in it. The new doesn't check your Mother manufactor for a bois Update or a way to bypass the tach on the MB header.

[DoDicK]

Thanks Soniclos... But, I think it is still important that the motherboard be able to check or monitor the fan.

Tachometer? can I just make one for my new fan or perhaps, disassemble the old fan and place the Tachometer on the new...??? Any other ideas... Thanks

[cyril1]

Basically the old fan works like this. The third wire on the fan is connected to 2 places on your fan. One spot on the rotor of the fan is electrically connected to Ground. When that place on the rotor of the fan passes one of the 2 spots connected to the pulse wire then it sends a ground out the pulse wire. This will happen twice per revoution.
On your MB there is a circuit that looks for a steady stream of grounds and opens. If it does not see them but sees a constant ground or constant open instead it raise an alarm.
I wish I could tell you that you could take parts off one and put on the other but I do not think you could get that to work. The best I could do is send you a circuit to fool the MB into thinking the fan is still there but then you would never know if the fan quits.
My recommendation is to take the fan back to the store if you can and buy a good 3 wire fan. By the way the way the fan works is a little more complicated than described above but I simplified it because the concept is more important than the actual description.

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600 duron@1000mhz(10x100FSB)
Abit kt7 raid
256MB Corsair Cas2
Asus TNT2 (untill the LE comes)
SoundBlaster Live Value

[DoDicK]

"The best I could do is send you a circuit to fool the MB into thinking the fan is still there but then you would never know if the fan quits."

You're right... but, important is keeping the cpu cool(regardless of knowing if the fan works or not), after all the motherboard still can track thermal changes. Correct me if I'm wrong.. ;=)

Anyway, I'll probably use that 2 wired fan somewhere else. . . Better be sure than a fried chips...

Again...Thanks

[cyril1]

The MB sensor is usually a ways away from the CPU. You could probably fry bacon on that thing by the time it picked it up. The MB sensor is usually lower in height also and since heat rises... well I think you get the picture.

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600 duron@1000mhz(10x100FSB)
Abit kt7 raid
256MB Corsair Cas2
Asus TNT2 (untill the LE comes)
SoundBlaster Live Value