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Thread: cpu fan not detected!

  1. #1
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    cpu fan not detected!

    hello, i was recently booting up my computer and during POST i got a messege stating that my CPU fan not detected! so i went to look at it and sure enough, it wasnt spinning. it would need a little boost and it would start right up. I have an extra fan lying around the house so i put it in, plugged it it and booted it and the fan springs bak to life. its even fasted then the first one so good, i thought, it works but now i still get that POST error even though the fan is working. I tried going into my bios to disable it but there is no option on it, then i tried taking out the cmos battery to reset it and left it out for a few and put it bak in and still, same error. i dont know what else to do, any help would be appreciate it, thank you

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    Wiredwrx's Avatar
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    Quote Originally Posted by jdiazj1
    hello, i was recently booting up my computer and during POST i got a messege stating that my CPU fan not detected! so i went to look at it and sure enough, it wasnt spinning. it would need a little boost and it would start right up. I have an extra fan lying around the house so i put it in, plugged it it and booted it and the fan springs bak to life. its even fasted then the first one so good, i thought, it works but now i still get that POST error even though the fan is working. I tried going into my bios to disable it but there is no option on it, then i tried taking out the cmos battery to reset it and left it out for a few and put it bak in and still, same error. i dont know what else to do, any help would be appreciate it, thank you
    The only thing I can think of is that the new fan is a 2 pin design, and not a 3 pin design. THe third pin is how the MB knows that the fan is spinning. Mind you, I have never seen that error before, but that is all I can think of. Also, tell us mosre about the setup. What MB. Is the CPU removable? Did the original fan come with the setup. perhpas you need an exact replacement.

    Otherwise, I have no ideas.

    Michael
    ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

  3. #3
    FLAC evandude's Avatar
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    yes, as wiredwrx said, the mobo is looking for the signal on that third pin. If the new fan doesn't have that sensor pin then the mobo is not going to be happy. one other minor question, you DO have the new fan plugged into the same 3-pin header on the motherboard, the one specifically intended for the CPU fan, right? (not powered off a molex or anything like that)

    if your new fan is lacking that sensor wire, there are a few options: get a new fan with the required sensor, fake it by running the sensor wire from another fan in the system to the mobo CPU fan header (would require that you have another fan in the system that actually has the sensor, and is running all the time as well), or if you are into electronics you can make a simple oscillator (a basic 555 timer circuit would do it) to output a fake rotation signal to that pin. either of the 'faking' options is kind of bad in that if the cpu fan really does die in the future, the computer won't know it; but at least it would let you get by until you can buy and recieve a new $2 fan in the mail.

    Another really crappy option (which I've done as a bandaid fix on a computer I didnt' care about) is to take a standard 80mm case fan, and put it a couple inches above the faulty CPU fan, blowing down onto it... the case fan forces the CPU fan to rotate so it won't fail to start spinning, and even if the CPU fan dies completely at least still gets some airflow down through the CPU heatsink.
    But don't take it from me! here's a quote from a real, live newbie:
    Quote Originally Posted by Viscouse
    I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
    eegeek.net

  4. #4
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    thanks for ur fast replies. lol, thats funny, using the case fan to 'jump start' the other one. well, the replacement fan is a 3 pin fan and its the same size and power input measurement as the one that i am replacing. the only difference is that the connection is a little different then from the original but it still fits in the 3-pins from the mobo. its a dell gx260 mobo. hmm, maybe tricking it might help but i dont know why its not detecting it if its a 3 pin fan, hmm! any other suggestions, thanks

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