Chassis fan running while PC turned off

By frankie4260
Sep 11, 2010
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  1. I am rebuilding a PC and as soon as I plugin the power the fan starts spinning. I have not turned on the power yet because I am concerned something is not wired properly. Please advice!
  2. hughva

    hughva TS Rookie Posts: 58

    Which fan?
    You're probably right, but it's hard to say if this is a problem with the fan itself or a short somewhere else.
  3. SBHack

    SBHack TS Rookie Posts: 24

    Check your PSU output to connector on MOBO - pin-out to make sure your voltage is correct in every location according to the MOBO's documentation. Why the rebuild? What was wrong before you started and what have you done toward correcting it.
  4. frankie4260

    frankie4260 TS Rookie Topic Starter

    Thanks for your replies. I am referring to a rear 120mm tricool fan which came with the chassis.

    What I am actually doing is building one good PC out of two defective ones. One PC had a bad motherboard and the other one had a crashed hard disk. So I am taking the best components from the two PCs to build the one in question.

    So as soon as I plug in the power but before I turn the PC on the fan rans in an intermittent manner. I also noticed that at the same time the light in the DVD player also is turned on/off intermittently. I've checked every connection twice.
  5. hughva

    hughva TS Rookie Posts: 58

    Disconnect this fan and see if the DVD light still blinks. Do the reverse also to isolate this problem.
  6. frankie4260

    frankie4260 TS Rookie Topic Starter

    I disconnected the fan and the DVD light still blinked. I then did the reverse but the fan still came up intermittently. I've tried disconnecting other components but the same thing continues to happen. :(
  7. captaincranky

    captaincranky TechSpot Addict Posts: 11,456   +1,759

    There's a possibility that this is caused by a bad PSU. Perhaps the ACPI is not functioning correctly. If possible substitute another PSU, if only to rule it out as a possibility.

    Are these fans running at full speed? It is possible that you could have a 5 and 12 volt lead crossed somehow, since the +5 volt is hot even during S-3 sleep.
  8. frankie4260

    frankie4260 TS Rookie Topic Starter

    I'm glad I followed your advice and substituted the PSU! Definitely, there was something wrong with it as the pc worked as expected with the substituted PSU. Thank you! The only bummer is that the PSU that I removed was a 450W and the one I substituted it for is only 350W.

    Thanks everybody for the input and suggestions which were a great help in troubleshooting this issue!
  9. captaincranky

    captaincranky TechSpot Addict Posts: 11,456   +1,759

    Meh, better a working 350, than a broken 450. As long as you don't harbor any delusions of video card grandeur with the smaller PSU, it should be fine.

    If you're in the market for another PSU, this Antec will run many current mid-line video cards; EA380D 40 bucks, w/free shipping, 30 bucks after MIR. The 380 watts is the actual output, not some tricked up BS.

    Anyway, you're quite welcome, glad you're up and running. :)
  10. frankie4260

    frankie4260 TS Rookie Topic Starter

    I'm probably ok with the 350W PSU since the PC does not have a video card. Thanks for the tip on the Antec PSU. I might go ahead and get it today before the MIR expires.

    Thanks again!!

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