Yosemite not working on Thunderbolt Display or iMac as external display

Discussion in 'OS X Yosemite (10.10)' started by Philly-GUI-Dude, Jul 30, 2014.

  1. Philly-GUI-Dude macrumors newbie


    Sep 5, 2009
    My MacBook Prop (late 2011) has worked just fine on my Thunderbolt Display since I installed Yosemite since day 1 and starting yesterday it stopped.

    When I sya it stopped working I mean the following:
    1. Display is black
    2. MacBook Pro does recognizes it
    3. The FaceTime camera still works
    4. The USB and network cable still works
    5. The power cable still works
    6. Bypassing the Tunderbolt Displays cable with my own Thunderbolt cable does exactly the same thing
    7. I don't see ghosting, but I do see ghosting on my iMac

    I would assume it with was my Thunderbolt Display, but it actually stopped working on my 27" iMac (2014) used as an external display using a Thunderbold cable since i installed Yosemite. The iMac as external display worked fine with Mavericks.

    IF I connect my MBP to my Dell Display using a DisplayPort to DVI cable, it works just fine.

    Any idea? Hope I gave all my details! Thanks!
  2. opfor macrumors newbie

    Jul 27, 2014
    I have a MPB late 2011 here and a Thunderbolt display. It seems to be working fine so far. If you give me some instructions I can try to reproduce.

    Have you tried switching to mirror display, etc just to see if something appears on the screen?
  3. Cythth macrumors regular


    Feb 24, 2013
    Lake Jackson, TX
    Do you have any other TB devices to test if it's the hardware on your machine?
  4. Philly-GUI-Dude thread starter macrumors newbie


    Sep 5, 2009
    Hey opfor, I did try to mirror on my iMac 27" using the Thunderbolt cable to use it as an external monitor, but all is see is an almost black screen. If you tilt the screen and look really close, you will see everything is there and that it is working. I'm not sure if this is called ghosting? Its as though the backlight is not on. BUT my iMac works just fine!

    Any idea? I used to use the iMac as an external monitor with my MacBook Pro with Mavericks just fine.
  5. Philly-GUI-Dude thread starter macrumors newbie


    Sep 5, 2009
    I have attached a photo of my iMac being used as the external monitor using the thunderbolt cable connected to my MacBook Pro running Yosemite

    Attached Files:

  6. Philly-GUI-Dude thread starter macrumors newbie


    Sep 5, 2009
    So I tested an early 2011 MacBook Pro on my Thunderbolt Display, and it wasn't working for it either, so I 'm not sure now that it is Yosemite, it might just be a coincidence that it stopped working.

    But on my iMac, using it as an external monitor for my late 2011 MacBook Pro with Yosemite, the image I posted in the last post, this started when I installed Yosemite.
  7. cmb650 macrumors newbie

    Jul 26, 2012
    Have you tried pressing command-F2 (command-fn-F2)? That just solved it for me, had the same problem with an external screen not working anymore for an iMac and came across http://support.apple.com/kb/PH19038

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