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  1. #1
    27 Inch Mid 2011 iMac Target Display Bug
    I'm trying to use a mid-2011 iMac as target display with early-2013 MBP Retina as the source. After logging in on the MBP and connecting both devices with a new thunderbolt cable, iMac screen goes dark after pressing command-F2. This is intermittent, around 50 percent of the time it will work as intended, then the other 50 will not work, requiring me to shut down the iMac, restart it and try again.

    I've tried multiple solutions from threads and nothing really helped. I tried different thunderbolt ports and cables just in case one doesn't work well, nothing happens still. Clicking on 'detect display' in system preferences - Displays doesn't do anything either. Both computers have their own latest software updates, conditions are pretty good, no idea why it's not working. Tried to use gfxCardStatus on MBP to select certain graphics card, still doesn't work. My MBP is plugged into the wall too. SMC and PRAM have been reset on both computers, new user accounts have been created on both computers, and even the iMac OS has been erased and installed.

    What I do know is my iMac does go into Target Display mode, because when I exit by pressing command-F2 while the iMac screen is blank there is a brief blue screen then the normal desktop or login screen. I have also confirmed that when the blank black screen is present, the mbp does register that it is attached to another display. We have two of these iMacs in the office and they both exhibit the same problem, also we have multiple macbooks in the office and each one exhibits the same problem.

    Anyone had similar issue? Any other ways I could solve this problem? Thank you!

    Both devices are on latest OS Mojave. It's a 27 inch mid 2011 iMac.

  2. #2
    27 Inch Mid 2011 iMac Target Display Bug
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
    Posts
    57,754
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 7+, iPhone 8, Numerous iPods, Mojave
    Welcome to our forums.

    Both devices are on latest OS Mojave. It's a 27 inch mid 2011 iMac.
    Part of the problem may be because your Mid 2011 iMac according to Apple can only run macOS 10.13.6 (High Sierra) and not Mojave. If you performed a work around to install Mojave, all bets are off with regard to Target Display mode. What happens if you revert back to High Sierra 10.13.6? Does it work then?

  3. #3
    Quote Originally Posted by chscag View Post
    Welcome to our forums.



    Part of the problem may be because your Mid 2011 iMac according to Apple can only run macOS 10.13.6 (High Sierra) and not Mojave. If you performed a work around to install Mojave, all bets are off with regard to Target Display mode. What happens if you revert back to High Sierra 10.13.6? Does it work then?
    Hey thankyou for getting back to me so quickly. I really appreciate it. I just ran out and checked the iMac's in question are actually Late 2013 27 Inch. Apologies for the incorrect information in my previous post.

    Hope you can help.

    Edit: Thanks for the warm welcome. Lovely to be here

  4. #4
    27 Inch Mid 2011 iMac Target Display Bug
    chscag's Avatar
    Member Since
    Jan 23, 2008
    Location
    Keller, Texas
    Posts
    57,754
    Your Mac's Specs
    2017 27" iMac, 10.5" iPad Pro, iPhone 7+, iPhone 8, Numerous iPods, Mojave
    Thanks for the correction. Looking over what you stated above, it appears that you're doing everything correctly (according to Apple's instructions). It should work.

    The only thing I can think of is either a cabling or connection problem. I know you said you tried different cables but there is always a possibility that it could still be the problem.

  5. #5
    Thanks chscag for the reply, I'll give another thunderbolt cable ago anyway as i've just purchased a few new thunderbolt cables for the company. So i'll open one up and see how it goes. All Cables we've used so far have been genuine apple also.

    The only thing I can think of is it's some form of bug that has slipped through the cracks. I don't know if it would be related but i did notice that the Apple Thunderbolt Displays that had a firmware update released for them titled "Thunderbolt Display Firmware Update v1.2" and to quote the Apple website this is what it addresses. "This update improves reliability when connecting devices to the Apple Thunderbolt Display, and addresses a rare issue that may cause the display to go black. "

    It seems that that is the exact issue I am having with 2 seperate iMacs. I wonder if this is a bug in some of the iMacs that are able to do target display mode and Apple have not gotten around to resolving it?

    I have noticed a handful of people online and in forums who have had the same issue with no resolution.

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