OSX 10.6.3 scrambles video on MacBook screen when external attached


macrumors newbie
Original poster
Mar 12, 2010
As a teacher I use a projector all day long. After upgrading from 10.6.2 to 10.6.3 last night without incident I was surprised to find out in class today that the screen on my MacBook scrambles when I attach the projector and go into slideshow mode in PowerPoint. Exiting slideshow doesn't fix it. Unplugging the projector does. I soon discovered that it's not limited to slideshows. My screensaver triggers it too. So does going full screen in Quicktime Player. Basically anything going full screen when the projector is plugged in does it.

I just tried it at home expecting the same results, but my external monitor doesn't trigger it. Hmmm, I'm using a DVI connection to the monitor whereas the projector is VGA. Does that sound like a driver issue? If so, why is the picture just fine on the external display, but the internal screen is messed up?

I don't understand. I see others are having display issues too. Has anyone found the answer?


macrumors newbie
Apr 2, 2010
Hey mpolda,

I'm having almost exactly the same issue on my macbook after upgrading to 10.6.3.

I have a Mini-DVI to RCA/Svideo adapter that I use with my macbook to watch videos on my TV.

Normally, when watching a video, I can make it fullscreen and have it output perfectly to the TV and simultaneously to my mac. Now, after 10.6.3, as soon as I hit fullscreen in either VLC or Quicktime, it immediately scrambles the screen on my mac but it leaves the output TV untouched.

Only after unplugging the adapter will I get unscrambled video back on my macbook.

Anyone have any ideas?


macrumors newbie
Apr 7, 2010
Same problem here

Upgraded over spring break to 10.6.3 and video scrambles on full screen. Powerpoint also unless I use presenter tools. What's going on here.


macrumors newbie
Jun 13, 2010
Sardinia, Italy
same here - mirroring is involved

I have the same problem.
My laptop is connected to an external screen. All is well until the screen saver starts. Then the LCD screen scrambles.
However, if I disable mirroring, the problem disappears.

The trouble is that I only disable mirroring when I am displaying a presentation. Normally, I let mirroring on and use the external screen, without even looking at the LCD.

Anyway, I can arrange my applications in the big screen, at least until this problem is solved.



macrumors newbie
Aug 10, 2011
I have the same symptom with the scrambled MacBook Screen:( whenever I connect to my Toshiba plasma TV via the DVI connector and invoke Full Screen Mode when playing a movie using either the latest Quicktime Player or VLC. I haven't explored other actions that might result in the same symptoms.
However, the movies play just fine on the big screen TV and when the DVI connector is removed, things return to normal on the MacBook. Still, I want this corrected.This defininietly started immediately after the 10.6.3 combo upgrade.