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igmackenzie Level 4 (2,285 points)

My iMac won't go to sleep.  If I leave it on, it only ever puts the display to sleep after the designated time, but the HDD never goes off.

If I select Sleep from the Apple menu in the top left, the display goes off, then the HDD powers down.  Then after a second or two, it all comes back to life.

Any help appreciated.

 iPhone 4 32Gb,  AppleTV2,  iPad 2 64Gb 3G,  iMac 27" 3.4GHz
  • den.thed Level 7 (25,980 points)
  • igmackenzie Level 4 (2,285 points)

    Thanks for that. I had already looked at that and it doesn't help at all.

    1) I tried disabling all sharing options

    2) unchecked 'allow Bluetooth devices.....'

    3) Spotlight is not indexing

    4) tried disabling time Machine

    None of these had any effect.

    Any other thoughts?

  • igmackenzie Level 4 (2,285 points)

    OK, I sorted it out.  It was an external USB powered hub that I'd forgotten was in there!

    Thanks a lot.

  • den.thed Level 7 (25,980 points)

    Ah' an incompatible USB device!


    If you really need the extra ports try a self-powered Mac compatible Belkin hub. I leave three different camera cables and a cable for my iPod's n iPad plugged into my Belkin 7 port all the time for quick easy access.

  • igmackenzie Level 4 (2,285 points)

    Thanks. Just ordered one from Amazon UK. £13 with free postage.

    This is the one, right?

  • igmackenzie Level 4 (2,285 points)

    I'm not out of the woods yet.

    Although when I select 'sleep' from the menu it works, when I came back to my Mac this morning, the HDD was clearly on.

    Looking at TIme Machine, it would seem that it still runs during the night.  Now I don't know if that relates to having Outlook constantly running, as it also seems to defy Sleep and accepts emails being received throughout the night.

    Is there not a setting that can disable this activity without shutting down TM and Outlook?

    I never had this problem when I was on Windows!

  • den.thed Level 7 (25,980 points)

    Personally I don't use Outlook or any other MS Office products, however any open and running application (Outlook) that is accessing the Hard Drive will prevent computer sleep. Re-read the following sections that I have highlighted in red from that Sleep Article above, note that (downloading large files and listing to iTunes) are being used as examples.


    Sounds like Time Machine is doing what it should do (backup every hour when the system is up), however the External HD or another USB device could also be waking the iMac.



    Why doesn't the computer go to sleep at the expected time based on Energy Saver settings?

    You can configure Energy Saver preferences to set your computer to automatically sleep after a specified period of time; an internal counter called a "sleep timer" monitors the amount of time your computer has been inactive. When the counter's time matches the amount of time you specified, the computer enters sleep mode and displays a pulsing power light.  (pulsing light on the older iMac's)

    Some things reset the sleep timers, preventing the computer from sleeping:


    • Hard drive access (even if you're not using the computer, a running application might be accessing your drive, such as when downloading a large file or listening to music in iTunes)
    • Moving the mouse or using a portable Mac's trackpad, pressing a mouse button, or pressing a key on the keyboard
    • Some System Preferences settings (see below)
    • Open applications (see below)
    • Input devices (see below)
    • Expansion cards (see below)
    • Additional drives, such as USB, FireWire, DVD, or CD drives (see below)


    In order to figure out what is waking or keeping the iMac awake, your going to have to eliminate them one by one and test it over time.

  • igmackenzie Level 4 (2,285 points)

    Thanks again.

    I'm afraid I'm confused. That list is a selection of events that prevents the computer from sleeping.  My problem now, is that it is woken from sleep.  Now, I can sort of accept that running apps may cause this - even then I would expect that the system should be able to detect a sleep state and not receive emails - but why on earth would TM kick in when the system is sleeping, and there is nothing to back up?

    I wouldn't have expected to have to shut down every running process when putting the computer to sleep.

    Surely every TM user or anyone running an email client must face this issue, or is this somehow unique to me and my configuration?

  • den.thed Level 7 (25,980 points)

    The trick is in trying to pin point what caused it to not sleep in the first place or as now in your case what re-awoke it. I think that your issue may now be related to ether a main power fluctuation or a connected USB devise like your printer, your TimeMachine drive, or something of that nature? To briefly explain, if the iMac is sleeping and there is even the slightest power fluctuation from your mains or anyone of the USB devices connected, then the iMac can and will wake from sleep.


    1. Go to: Applications > Utilities > open the Console and select All Messages.

    2. Now scroll back in the Logs until the time that you put the iMac to sleep.

    3. Then look at the next entry to see what woke the iMac.



    Last night I slept my iMac from the drop down menu at 10:14:34 PM

    6/4/11 10:14:34 PM kernel System Sleep

    then I woke my iMac at 5:10:22 AM today by clicking my USB mouse

    6/5/11 5:10:22 AM kernel Wake reason = USB1


    You are looking for is the Wake reason = ? in your Console logs.

  • igmackenzie Level 4 (2,285 points)

    After the last System Sleep, there are the following messages:


    04/06/2011 21:47:10 airportd[359] process_dlil_event: Set power failed err = -3903 (Operation not supported)

    04/06/2011 21:47:10 kernel Wake reason =

    04/06/2011 21:47:10 kernel System Wake

    04/06/2011 21:47:10 kernel /drv/ MacModule.cpp:261   powerStateWillChangeTo: flags=82 stateNumber=4

    04/06/2011 21:47:10 kernel /drv/ MacModule.cpp:262   powerStateWillChangeTo: found flag=kIOPMPowerOn (2)

    04/06/2011 21:47:10 kernel /drv/ MacModule.cpp:267   powerStateWillChangeTo: found flag=kIOPMRestartCapability (80)

    04/06/2011 21:47:10 kernel /drv/ MacModule.cpp:261   powerStateDidChangeTo: flags=82 stateNumber=4

    04/06/2011 21:47:10 kernel /drv/ MacModule.cpp:262   powerStateDidChangeTo: found flag=kIOPMPowerOn (2)

    04/06/2011 21:47:10 kernel /drv/ MacModule.cpp:267   powerStateDidChangeTo: found flag=kIOPMRestartCapability (80)

    04/06/2011 21:47:10 kernel Previous Sleep Cause: 5

    amongst many others obviously!

    Is there a clue there?

  • den.thed Level 7 (25,980 points)

    I'm no expert at reading the logs, but actually it looks more like it restarted than woke up from sleep.


    At this point I would:


    1. Reset the SMC

    Intel-based Macs: Resetting the System Management Controller (SMC)


    2. Then go to: System Preferences > Energy Saver and uncheck the box "Start up automatically after a power failure"

    Screen shot 2011-06-05 at 9.12.53 AM.jpg

    Then if you find it off after a period of sleep, it probably lost power during that time.

  • igmackenzie Level 4 (2,285 points)

    Thanks again.  I'll try it tonight and see what happens.

    Sorry, should have said, the 'start up after a power failure' had never been set, so I guess that wasn't the answer.

  • den.thed Level 7 (25,980 points)

    Keep us posted...

  • igmackenzie Level 4 (2,285 points)

    OK, it seems to work now, with no need to shut down any apps, but only if I select 'sleep' from the top left Apple menu.  However, if I just let it 'sleep' via Energy Saver settings, i.e. after 15 minutes, it is only the display that turns off, no HDD power down.

    Why would that be?

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