iMac 2.4Ghz USB Power not working

Discussion in 'Mac Basics and Help' started by Paul Ashton, May 14, 2009.

  1. Paul Ashton macrumors newbie

    Paul Ashton

    May 14, 2009
    I have an iMac 2.4Ghz 24" about 18 months old. After a visitor's mains powered hard drive (which was later shown to be already faulty!) was connected I lost the power to the USB bus inside the iMac. I can still use devices that need power with an USB port expander but this is far from ideal.
    USB data is working fine as is the firewire port. Simply the power to the USB.

    I have reset the PRAM but not yet reset the Power Management Unit.
    I assume there is no physical fuse for the USB power internally as I have not seen a reference to one anywhere.

    I am sure I am not the first with this problem, Should I reset the PMU? What else? Are the USB and their power integral to the motherboard?

    wow, my first ever question and no-one can answer? :(
    More info then: on start up I get the error message

    USB Over Current Notice
    A USB device is currently drawing too much power
    The hub it is attached to will be deactivated

    I get this error message even when NOTHING not even keyboard is plugged in (so its not that faulty keyboard error). There really is no power at the USB ports - but data is working
  2. Rhalliwell1 macrumors 6502a

    May 22, 2008
    The Bluetooth, IR Receiver and iSight are all on the USB too. Maybe the WiFi too? One of these could be causing the problem. You can turn the bluetooth off in it's preference pane and block the IR in security, i don't think that will do anything though. You need to disable them. Anyone know how? As for the iSight.... i don't have a clue i am afraid.

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