I have a Macbook Pro running Snow Leopard, and sometimes it does not go to sleep per the Energy Saver settings. I’ve asked about this multiple times at the Genius Bar, but no one seems to have a consistent explanation. One Apple Genius thought that my router was keeping the Macbook Pro awake, but it did not sound likely to me. As an example of what happens, if I leave my iPod syncing at night, the next morning I notice that the Macbook Pro has not gone to sleep, contrary to expectation. I’ve re-tested this with the Sharing Services in the Energy Saver tab set to “Never,” but there was no impact. I’ve read the Apple Support article on this, but it does not seem to give definitive information:
http://support.apple.com/kb/HT1776
— Vlad
I'd try some more tests to determine what it must be. Set the sleep time to something very short. Then try it with no applications running. Try removing items from the Log In items in your account preferences. Try it with each of your USB devices disconnected. Try it without any shared drives or servers mounted. Etc.
Eventually, hopefully, quickly, you will find what software or device is causing it.
Do you have a wireless mouse plugged in? I used to have this issue and found out it was my wireless mouse crawling slowly across the screen.
Thanks, great tips! I did Gary's recommended tests, and I narrowed the culprit down to my USB hub, even though it has it's own power supply. Interestingly, the USB powered fan does not prohibit sleep mode.
Mac Pro in sleep mode wakes up every hour. Why is this?
Most likely has to do with something connected: network drives, peripherals, bluetooth devices, etc.