7 Replies Latest reply: Feb 21, 2012 9:22 AM by ChazThePhoenix
petedragon Level 1 Level 1

I have a mid-2011 Thunderbolt 21.5" iMac. A secondary monitor is connected to the iMac with a Mini DisplayPort-to-HDMI cable (a single cable, not an adaptor and cable).


When I was running Snow Leopard, the monitor worked just fine. After upgrading to Lion, the second monitor just has a black screen, and quickly goes into power save mode.


I have already tried resetting the NVRAM (as described here: http://support.apple.com/kb/HT1379) and resetting the SMC (as described here: http://support.apple.com/kb/HT3964).


Has anyone seen this problem? Any other suggestions for solutions?

iMac, Mac OS X (10.7)
  • John Kitchen Level 3 Level 3

    This is not because your primary monitor is in fullscreen mode is it?

  • petedragon Level 1 Level 1

    No, the primary display (the built-in iMac display) is not in fullscreen mode.

  • John Kitchen Level 3 Level 3

    I was thinking of a different issue.  I recall a posting somewhere about HDMI incompatibilities, but I don't recall the story.

  • GautierRouen Level 1 Level 1

    same here, just performed the upgrade to Lion and my secondary Samsung screen (direct HDMI cable) do not work anymore (I have a mid 2011 iMac 21.5'').

    I have tried the tricks mentioned on the following discussion:

    No Signal on HDMI TV After Lion Upgrade

    ie open terminal

    cd /System/Library/Displays/Overrides/DisplayVendorID-410c/

    sudo mv DisplayProductID-0  DisplayProductID-0.old

    Reboot after entering the commands


    But it is not working, the developper clearly messed up the video output in Lion OS!!!

    Let me know if you have a solution, I am reduced  to single screen use in the meantime... and regret the upgrade...


  • kp3460 Level 1 Level 1

    same here - also tried everything and cannot make it work

  • petedragon Level 1 Level 1

    Not sure if this will help any of you, but this ended up being a cable issue. I was using a Mini DiplayPort-to-HDMI cable, which worked just fine before the upgrade. After the upgrade, it did not work. After exhausting all of my other options, I tried a MDP-to-HDMI adapter combined with an HDMI cable, and this worked just fine. I know my cable was functional, because it worked just before the upgrade and I did not touch it. Apparently, the MDP-to-HDMI cable is actually unlicensed. My best guess is usage of these unlicensed cables has been disabled.

  • ChazThePhoenix Level 1 Level 1

    one thing I learned today is that the mini display port plug can go in two ways...but one way it wont work. Usually a plus goes in one way only....


    ask me how I know and how long it took me to figure this out......