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I have my Mac Pro (Cyrus) configured not to fall asleep completely but to let the screen sleep when not used for half an hour. I also use the keyboard shortcut for forcing the display to sleep.

However, sometimes, for a few weeks the screen just refuses to sleep and the login alert box appears immediately after the sleep is supposed to start as if somebody violently moved the mouse or pressed a key. After a few weeks the behaviour changes again and sleeping works, for another few weeks. It's periodic.

How can I force the screen to sleep without waking up all the time?

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1 Answer

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I have discovered that 100% of the times that this happened to me, it was because I either had:

  1. A USB (or Firewire) peripheral connected that was pooling the bus and for some mysterious reason caused your behavior.

  2. I accidentally moved the mouse (or the table where both mouse/key lie); small vibrations caused the mouse to register movement and that was enough to wake the box.

I don’t know if this is your case, but whenever you’re in the “it wakes up!” cycle, try to disconnect everything and use the keyboard shortcut with surgeon precision and softness and see if it changes.

Additionally you might want con check the Console Output of the logs to see if there’s an error going on while your invoke your sleep screen shortcut.

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#2 is impossible because the mouse absolutely doesn't move every minute. But #1 is very possible. I have many USB devices and I wonder if there is a device that just happened to be connected whenever this the screen refuses to sleep. – Andrew J. Brehm Oct 21 '10 at 14:43
@Andrew do the obvious now, try disconnecting them all and start one by one :) – Martín Marconcini Oct 21 '10 at 15:40
I checked console output and found that the most likely suspect (was talking about waking things) was my EyeTV adapter driver. Ever since I found it, the display sleeps again although I haven't changed anything. Perhaps starting and exiting the EyeTV application did the trick. – Andrew J. Brehm Oct 22 '10 at 11:05
@Andrew Glad you found the fix. :) – Martín Marconcini Oct 22 '10 at 13:31

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