In case it helps, here is what seems to have worked for me...
I just bought 3 Mac Air with 8GB, 256.
I've set them up slowly over the last few days, tranfering files, etc. Had no issues at all for about a week.
Today I did 3 things, and 2 of the laptops starting getting the black screen issue for the first time (My wife has the 3rd and is away with it - no reports yet)
- I switched my Wifi/router to a new 2TB Time Capsule
- I turned on TimeMachine, and backed up to the TC
- I also turned on photo stream.
To elliminate magnetic/physical stuff, I stayed perfectly still and timed the issue. it would go black 30 seconds exactly after I hit the key to wake it (I have it on auto login so no login page)
So I systematically turned things off, and woke it again each time.
- wifi
-bluetooth
- time machine
- Airplay mirroring
etc... Each time, it still went black exactly 30 seconds after waking
Then I went into Energy Saver settings, and one by one:
Turned of Enable Power Nap... it still wen black after 30 se
Turned off "Wake for Wifi" still blakc
Turned off "Put hard disks to sleep..." still black after 30 seconds
Then I CHECKED "Prevent computer from sleeping when display is off"
NO MORE BLACK SCREEN!
Then I unchecked it! STILL NO more black screen.
I still havent had a screen issue since (fingers crossed).
Does anyone else want to try this and let us know if it helps? (I was plugged in the whole time).