Two External Displays in Yosemite

Discussion in 'OS X Yosemite (10.10)' started by SeberrY, Sep 9, 2014.

  1. SeberrY macrumors newbie


    Oct 10, 2011
    Hi everybody...

    I just got a brand new 21.5" iMac, and I connected two external displays through Mini DVI --> HDMI cables. These two displays are each connected to the two Thunderbolt ports on the iMac.

    When I started the computer for the first time and set everything up, all three monitors (including the iMac's internal one) worked fine, but when I upgraded to Yosemite, I can only get it to recognize one external display at a time (whichever was plugged in first).

    Anyone have experience with this? I'm making a mountain lion USB as we speak to downgrade... It's a shame!

    I've tried restarting, resetting SMC, and resetting the PRAM.
  2. Kyle-K, Sep 11, 2014
    Last edited: Sep 11, 2014

    Kyle-K macrumors regular


    Aug 23, 2014
    Geraldton, Western Australia.
    You're running a non-released version of "Yosemite" So who knows how did you go reverting? Did everything work again?

    Requested a move to the "OS X Yosemite" Section of the board as its most likely better suited in there and I highly doubt it's a hardware issue.

    Notice: I wish people would use disk utility to add another partition and install Beta OSs in there.
  3. SeberrY thread starter macrumors newbie


    Oct 10, 2011
    Reverting went fine, and yes my two external displays work without a hitch. I realize it's beta software, so I hold no ill-feelings towards Apple... I'm just surprised this hasn't been fixed this late in the development of Yosemite. Now I'm looking forward to the public release.
  4. jmj8778 macrumors newbie

    Sep 11, 2014

    Just chiming in saying I've had the exact same experience. My dual monitors worked perfectly on Yosemite for 1.5 months and all of a sudden it's only whichever is plugged in first.

    Upgrading to developer preview 7 to see if that fixes things, already ran a number of fixes that are customary for mavericks machines with this issue to no avail.
  5. SeberrY thread starter macrumors newbie


    Oct 10, 2011
    Does the latest version (the GM Candidate) fix the issue for you?
  6. mmomega macrumors demi-god


    Dec 30, 2009
    DFW, TX
    I went from Mavericks to Yosemite DP1 with my iMac with 2 external displays and they have been working flawlessly since I connected them, wish I could help you. I've gone through every DP and never lost either display.:(

    Just on a 27" iMac with dual 27" Monitors connected MiniDisplay to HDMI.
  7. jmj8778 macrumors newbie

    Sep 11, 2014
    I ended up reverting due to this issue. I believe the last DP I was on was 7, but it may have been 8, and it was still not working.


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