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I have Mac mini with the latest Leopard + all patches. I've set it up for the monitor to go to sleep after 5 minutes of inactivity, but it just won't turn off.

The trouble started last week after I upgraded the RAM from 1gb to 2gb. Software-wise nothing changed.

Oddly enough, I have the same exact problem on my pc laptop. I suspected that the cat would just jump on the keyboard in the middle of the night and the monitor would wake up. But I locked the cat out of the computer room for the night and the monitor was still on in the morning. The cat denies all knowledge.

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Clearly your cat can pick locks. Seriously though, the monitor won't enter sleep mode at all or does it goes to sleep and then just wake up before it should? – Bryan Schuetz Aug 4 '09 at 10:50
up vote 2 down vote accepted

I have found similar problems from time to time: it may be a particular process or application which prevents the idle timer from kicking in.

Try quitting programs like VLC, Quicktime Player and the like.

A good test might be to restart the machine, and then see if it will allow the monitor to go to sleep. Then use ps or Activity Monitor to see which processes are running.

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It's true that Airport could be waking your computer, but then simply unchecking 'Wake for network access' box should fix this (see SysPref pane view below).

alt text

You may want to try a few tests like forcing your monitor to sleep by pressing SHIFT-CTRL-EJECT together. I have a login prompt screen after moving my mouse, but leaving it 30 seconds should automatically make your monitor sleep.

If these tips aren't helping and this seems to be a problem when using with a PC also, perhaps updating your monitor drivers?

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I've recently found what might be a reason for lots of will-not-stay-asleep issues with OSX.

Apparently, it is to do with Airport (WiFi) being connected:

It almost seems like the AirPort is failing to disengage itself when going into sleep mode. Then when it goes into sleep, the Airport awakens the computer to reestablish the network connection.

(from a discussion here)

And, there is a potential solution. Using Wireless Sleeper can fix the problem under certain circumstances.

I've only just started using it, but hopefully it will solve my issues like this that seem to have re-emerged lately.

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