Previous 1 2 Next 23 Replies Latest reply: Sep 25, 2012 9:55 AM by chicodaman
JBHLMH Level 1 Level 1 (0 points)



  I have a Mac Mini 2011 with a Thunderbolt/mini-DisplayPort and HDMI port. Before upgrading to Moutain Lion, I was running Lion Server.


I have two displays connected to the Mini:


                    - 19W" Acer LCD monitor connected via mini-DisplayPort -> DVI adaptor.

                    - Projector connected via HDMI -> HDMI.


These two displays used to work simultaneously as mirrored displays. I have them set to 720p. I could turn either on/off and the mini could switch between them.


Now that I have updated to Mountain Lion, the Mini will not recognize my LCD monitor, and the projector only flashes while it tries to accept the LCD display. Only way to get them both to work is to unplug the projector(HDMI) and plug the LCD into the HDMI(HDMI -> DVI adaptor). No more dual displays.


I would really like to get this working again and am not sure why the upgrade has taken this functionality away.


Any help is appreciated!



Mac mini, OS X Mountain Lion, 2011
  • malpatriota Level 1 Level 1 (0 points)

    Have you solved this issue?

    Im with tv lcd 19" samsung with hdmi - dvi connected to mac lion 2011 Mountain Lion but it doesn't work too

  • Littlelarry33 Level 1 Level 1 (0 points)

    I have the same issue. Everything worked fine in Lion but now, my Macs screen flashes blue as if its about to accept the sonnection with the secondary display but nothing happens and a second display isnt reconized in the system preferences.


    I'm on a MacBook AIr

  • coolcowman Level 1 Level 1 (0 points)

    I experience difficulties when I connect an external VGA projector through my Thunderbolt interface. The external screen seems to have a purple overlay resulting in an unviewable screen. First I thought it was the adapter, but changing it another it worked once, but after closing the lid and opening it again it gave the same bad results, help...

    Before I upgraded to Mountain Lion it worked without any issues.

  • chicodaman Level 1 Level 1 (15 points)

    Similar problem. I used to be able to plug and unplug my HDMI TV via Thunderbolt at will, with no issues. But lately I have to reboot the computer to get the HDMI chain to sync up. It may be a Mountain Lion issue. I can't figure out anything else that's changed.

  • Rich Strachan Level 1 Level 1 (0 points)

    I also have this issue. I really cant be bothered to downgrade to Lion again as I the thought of doiing all the data stuff gives me a headache.


    I managed to get it working for 1 session by doing a PRAM reset, but now it is back to flashing a blue screen on the Mac Book Air and nothing on the display,  The display does appear in my System Preferences as a TOSHIBATV. 


    In my system Info under display I have


    Intel HD Graphics 3000:


      Chipset Model:          Intel HD Graphics 3000

      Type:          GPU

      Bus:          Built-In

      VRAM (Total):          384 MB

      Vendor:          Intel (0x8086)

      Device ID:          0x0116

      Revision ID:          0x0009


    Color LCD:

      Display Type:          LCD

      Resolution:          1440 x 900

      Pixel Depth:          32-Bit Color (ARGB8888)

      Main Display:          Yes

      Mirror:          Off

      Online:          Yes

      Built-In:          Yes

      Connection Type:          DisplayPort


      Resolution:          1920 x 1080 @ 60 Hz

      Pixel Depth:          32-Bit Color (ARGB8888)

      Mirror:          Off

      Online:          Yes

      Rotation:          Supported

      Television:          Yes


    But nothing on the screen.

  • chicodaman Level 1 Level 1 (15 points)

    I wonder if Apple is aware of this? If not, maybe someone ought to check in with Applecare support to initiate a bug report.

  • Rich Strachan Level 1 Level 1 (0 points)

    I have a call scheduled tomorrow at 19:15 BST (which I will doubtless miss because my train will be late...)  I will let you know how I get on.

  • JBHLMH Level 1 Level 1 (0 points)

    That sounds awesome Rich. Let me know how you fare.




  • Rich Strachan Level 1 Level 1 (0 points)

    So typically I came home tonight (trains running on time) in good time and turned on the macbook in readiness for the call.


    After it had turned on I notice the TV is on standby so I turned that on.  Doing so I noticed the MB twitched to the blue screen, so I tried switching to HDMI2 on the TV and lo and behold it was working.


    I tried restarting the Mac Book and it stil worked.  Then the guy called.  After spending 5 minutes trying to flog me additional warranty on the hardware he told me he would have a look to see if there were any known issues.  He put me on hold for 5 minutes (presumably while he googled it) and then told me that next time it happened I should try a PRAM reset and an SMC.


    So in summary I would suggest try having the 2nd screen turned off before starting your mac and then turn it on once you have booted.  It worked for me.


    Good Luck.



  • Rich Strachan Level 1 Level 1 (0 points)

    Stopped working again.  Have tried various different boot/standby/poweroff/cableplugging sequences and I got it working once. Very annoying.

  • chicodaman Level 1 Level 1 (15 points)

    Rich Strachan wrote:


    Stopped working again.  Have tried various different boot/standby/poweroff/cableplugging sequences and I got it working once. Very annoying.


    Basically the same behavior here. After a reboot, I can plug in and unplug my monitor (TV) multiple times and it works perfectly. But when I use the computer for a certain amount of time for other tasks, the plug in the monitor, it won't sync. I see the HDMI handshake occur on an HDMI splitter I have connected for these debugging purposes, but the computer decides there's nothing it can connect to and no monitor or other external HDMI device can be made to work.


    But here's something interesting. I haven't yet determined what event(s) cause the HDMI connection to cease functioning when the external monitor is connected, but it can be corrected by logging out and back in, not just a full reboot. So the issue seems not to be a low-level system one that requires all drivers and system parts to be reloaded, but something in the higher-level components of the user software. I'll keep an eye on what's happening to see if something can be pinpointed.


    I understand the next OS rev (10.8.1) should have some Thunderbolt updates, so hopefully that'll remedy this. It's a pain to have to re-login each time I want to watch something from the computer on TV.

  • chicodaman Level 1 Level 1 (15 points)

    OK, I figured it out, at least on my machine.


    The 10.8.1 update didn't fix it, so I started digging a bit. LSS, I found out that my 15" Early 2011 MBP has two Graphic Proccessing Units (GPUs):  a discrete AMD Radion HD 6750M and a GPU integrated into the CPU, an Intel HD Graphics 3000.


    The computer should properly switch between the two, selecting the discrete AMD with the power connector plugged in (for better performance) and the integrated Intel GPU with the power connector disconnected (for better power savings).


    As far as I can tell, after moving to Mountain Lion, for some reason, after a while (maybe after sleeping, or some other activity, I don't have the patience to track it down), when the power connector is connected and the discrete GPU should be enabled, the integrated GPU is instead enabled.


    I didn't know this until I downloaded Cody Krieger's "gftCardStatus" (, which tells you which GPU is in use, and lets you specify which one you want to use.


    Turns out that the integrated GPU won't connect to my 1080p Vizio TV, but the discrete one will. So when the integrated GPU was activated (for some reason I don't yet understand), the Thunderbolt connection to the TV would fail.


    The solution: use "gfxCardStatus" to keep the discrete GPU enabled instead of the Intel integrated GPU. As long as the discrete GPU is active, the TV works. When the integrated GPU is enabled, the TV won't work.


    I may have some of the details wrong here, as I just discovered this and haven't examined it more closely. But for my purposes, I can easily fix the problem by selecting the discrete GPU using "gpuCardStatus", without having to restart or relog in. That's a relief.


    I'm still not sure why my computer decides to use the integrated GPU instead of the discrete GPU at certain times. It didn't before Mountain Lion. But at least I now have a fix.

  • JBHLMH Level 1 Level 1 (0 points)

    Thanks, but this doesn't help my problems with my Mac Mini.


    Can make it work on my Macbook now though. lol.

  • JBHLMH Level 1 Level 1 (0 points)

    So I am still having this issue.


    Things will work if I have the HDMI monitor on and then plug in the Thunderbolt monitor. Then I can turn on/off the thunderbolt monitor as much as I want and things will work fine (mirror mode and extended).


    Also it works fine if I have the Thunderbolg monitor on and plug in the HDMI monitor. Then I can turn on/off the HDMI as much as I want.


    Still, when I leave them both plugged in, turn off both, I can never get the Thunderbolt monitor to turn on. I need to unplug the HDMI every time.


    Nothing working yet. Hope we can find something.

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