I have an iMac, and because I program I prefer to use the extended USB keyboard.

Just as the batteries to my wireless mouse died, my USB keyboard inexplicably stopped working. I've been using this keyboard for months through previous mouse battery failures without incident.

Here's what I've observed:

  • The USB keyboard works fine when connected to my MacBook Pro. (The keyboard works.)

  • My iPhone charges when connected to the USB ports of the iMac. (The USB ports work.)

  • The USB keyboard works fine when connect to the USB port of my secondary Thunderbolt display, but only one of the three ports. (?)

  • When the USB keyboard is connected directly to the iMac, sudo dmesg produces two lines like this:

    AppleUSBHubPort[...]::FatalError - Port 2 of Hub at ... reported error ... 
    while doing setting port power

Where's what didn't work:

  • Rebooting in safe mode: sudo nvram boot-args="-x"

  • Deleting the Bluetooth wireless keyboard device and rebooting

  • Rebooting while holding Command-Option-P-R

I have an iMac running OS X 10.8.2 with a secondary Thunderbolt display.

  • Try it with a different user account. Also did you try fixing permissions?
    – kal-al
    Jan 29, 2013 at 2:53
  • Guest account has the same problem. Now none of the USB ports work for the keyboard. Also, sudo dmesg contains twelve lines that look like this: USBF: 27656.903 AppleUSBHubPort[0xffffff804d2cd400]::FatalError - Port 3 of Hub at 0xfa120000 reported error 0xe00002c0 while doing setting port power Jan 29, 2013 at 23:11
  • Do other keyboards work on that computer or is it unable to read any external keyboard?
    – kal-al
    Jan 30, 2013 at 2:36
  • The little bluetooth keyboard works fine. Jan 30, 2013 at 14:55
  • Maybe some internal cabling is broken or short circuited and the keyboard is drawing too much current.
    – jaume
    Jan 30, 2013 at 16:34

2 Answers 2


Hinted by similar discussions in related forums, I figure it's bad contacts. I fixed my issue by gently squeezing the keyboard USB to make it tighter. Be careful not to break it though. Just a gentle squeeze, so that it's about 0.5-1mm tighter should be all that's needed.

This would explain why new keyboards work fine for a while and why extension cords only help for a while only as well.


I have observed the exact same problem. However, when connecting the keyboard to the iMac via an extension cable, the keyboard works fine. I have experienced this consistently. Also, I had the keyboard changed because of this error; the new keyboard now (after some months) behave the same way. It is quite strange!

  • This looks as a bad contact at the female USB connector on the iMac side. Any brand new cable will work for a while (this is causing a surprising repair with an extension cable). But with time and repeated connection disconnection the bad contact will appear again.
    – dan
    Feb 2, 2014 at 15:52
  • Daniel, when this was happening to me, it would eventually happen to all the USB ports on the iMac, one after the other over a period of time, not just one. Feb 8, 2014 at 4:55
  • See also discussions.apple.com/message/26300976
    – robd
    Aug 11, 2014 at 11:34

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