Weirdest thing: Clip-on fan makes iMac's keyboard not working

Discussion in 'iMac' started by Robertus, Jul 8, 2013.

  1. Robertus macrumors member


    Feb 5, 2009
    the great state of O-H-I-O
    I have a late 2009 21" iMac. It gets so hot in the summertime that I had to buy a 6" clip-on fan to cool down the area of iMac. It is a cheap product that I bought at a bargain store.

    I positioned and clipped the fan in the back area of the stand where the iMac sits on, it titled at an angle where the fan can blow at the top part of the iMac. Turned it on at low power.

    So, for a while, I was typing away on a project on the iMac. Then the keyboard was not responding to my keystroking. Puzzled, I used the tab key to switch to a different app, not responding.

    BUT... the mouse is responding and I was able to move the cursor around on the screen, open or close the app. I checked to make sure the keyboard USB is firmly plugged in. Still no response from the keyboard with typing.

    I rebooted. iMac was working normally. I resumed back to my project typing. Clip-on fan is still blowing at the back of the iMac. Few minutes after reboot, the keyboard is not responding again. I thought this is odd.

    To be on the safe side, I turned off the clip-on fan. Rebooted the iMac and it's working normally (although I noticed screen flickering/dimming every once in a while). With the clip-on fan off, the keyboard is responding normally and I was able to work on my project for few hours. iMac is still hot. AC came on at a programmed time.

    Next day, I went back to my project for a couple hours before I turned on the clip-on fan. After one minute from turning on the fan, the keyboard stopped working! I always check to make sure the USB is firmly plugged in.


    I turned off the clip-on fan. Reboot the iMac, all is working normally. I removed the clip-on fan from the stand and am completely puzzled by the fact somehow the clip-on fan is causing the keyboard to the iMac to be not functioning!

  2. forty2j macrumors 68030


    Jul 11, 2008
    iMacs don't have a lot of free power laying around; the power supply is basically the bare minimum it needs to function. Chances are the fan pulled power away from the keyboard.

    If you need to use this USB fan, you may need a powered USB hub to plug it in to.
  3. Robertus thread starter macrumors member


    Feb 5, 2009
    the great state of O-H-I-O
    Interesting. Thanks!
  4. drambuie macrumors 6502a

    Feb 16, 2010
    Forty2j is correct, the cheap fan is probably marginally overloading the iMac's USB power capability. I would remove it before you damage the iiMac. You don't need to go to the expense of a powered hub, as there are inexpensive power bricks available with USB connectors for charging various 5 volt devices. If you have an iPad, it's power brick with 2.1 amp output at 5 volts should be sufficient for the fan.
  5. Bear macrumors G3

    Jul 23, 2002
    Sol III - Terra
    It could be too much power, or it could be an issue with how the fan's USB connector is wired.
  6. Big-TDI-Guy macrumors 68030


    Jan 11, 2007
    I do not see anywhere in the original post where he said the clip on fan is USB powered. Am I missing something?

    Also - the screen flickering / dimming sounds indicative of bigger problems, that could very well be heat-related.

    Ignoring the clip on fan entirely at this point I'd do the following:

    Download an app called "SMC Fan Control" - this program will show you the temps inside your iMac, and allow you to increase your fan speeds to keep it cooler. I'd suggest increasing the speed until you can just start hearing the fans - backing off to where you can't hear them again - and making that your "default" fan speed.

    Get some canned air / compressed air and blow out all the vents on the iMac (ideally with the fans running on high - to help stop the dust from re-settling again) In the absence of canned air - use a vacuum with a brush attachment - and create a good seal to the vents - so it draws the dust out that way.
  7. orangezorki macrumors 6502a

    Aug 30, 2006
    Could it not be that the fan (USB or not) is so poorly shielded that there is interference with the keyboard? Much more likely if it were BT, but still...

  8. Robertus thread starter macrumors member


    Feb 5, 2009
    the great state of O-H-I-O
    Thank you for pointing out something I forgot to add: the clip-on fan is not USB-powered, it was a two-prong plug to the wall.

    Thank you for your suggestions. I will certainly try this. I have iStat Nano app (the temps of my iMac are CPU A is 104 degree, GPU diode 142 degree, GPU Heatsink 137 degree, Ambiet at 74 degree, and Northbridge 139 degree).

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