Troubleshooting iMac Target Display mode

iMacIconXWhen Apple introduced its late-2009 iMac systems, it was clear the large built-in display on these systems could not only be used for the accompanying computer, but similar to the functions of Target Disk mode for hard drives, the display could be used for another Mac.

While Target Disk Mode requires you to restart the system into a special mode, the use of Target Display simply switches the monitor to accept input from an external source, rather than the running system, just as if you had unplugged it for alternative uses.

To do this, first check the model of your iMac to ensure it was made in late-2009 or later, and then simply press Command-F2 after connecting the systems with a compatible cable. Note that on most Macs, the F-keys are assigned to a system function by default, so you will either have to revert this in the Keyboard system preferences, or hold the “Fn” key in addition to the Command key before tapping F2.

When you press this hotkey, the system will remain running, but the display will now be accessible through the Thunderbolt connection of the iMac, smaller systems such as laptops to make use of the larger display with the use of a Thunderbolt cable.

Troubleshooting

1. iMac not switching to Target Display mode

If your iMac supports Target Display mode but does not enter it, then try resetting your iMac’s SMC. Additionally, for older iMac systems, be sure you are using OS X 10.6.1 or later. In addition, be sure your have first connected your iMac and secondary computer before entering Target Display mode.

Finally, be sure you have applied all software and firmware updates for your iMac that Apple has made available. To do this, go to the Apple menu and choose Software Update, and then install any updates available, especially those for SMC firmware or OS software.

2. Ensure compatible connections

Thunderbolt compatibility diagram

Thunderbolt connections can be used for displayport devices, but not vice-versa.

Even though Thunderbolt connections contain DisplayPort data, Target Display mode on a Thunderbolt-equipped iMac not work with DisplayPort connections. Therefore, if you have a DisplayPort-equipped Mac and wish to use the mid-2011 (or later) iMac’s display as an external monitor, you will not be able to.

For iMacs before the mid-2009 model, you will not be able to use a Thunderbolt cable for the connection, so ensure you have a proper mini-displayport cable. Note that the Thunderbolt and Mini-Displayport connections look the same, so differentiate these by the lightning-bolt symbol for Thunderbolt, vs the square bracketed symbol for Mini-Displayport.

3. Directly connect the iMac

While Thunderbolt supports daisy-chaining of devices, be sure to connect the iMac directly to the secondary Mac

4. Media and brightness controls

When in Target display mode, you should be able to adjust the iMac’s volume and display brightness; however, keep in mind these will be adjusted from the iMac’s keyboard, and not from the one connected to the iMac.

5. Sound not playing through the iMac

If you have Target Display mode set up but no audio is playing, then go to the Sound system preferences on your secondary Mac and ensure the iMac is selected as the sound output device.

37 thoughts on “Troubleshooting iMac Target Display mode

  1. Strod

    Hi. Tip #3 suggests you connect the iMac directly. I have two questions about that:

    – Is that mandatory? I.e., does placing the iMac behind other devices work sometimes, and the tip is meant just as a troubleshooting step?

    – If the iMac is connected directly, can you daisy chain additional devices on its other Thunderbolt port?

    1. Topher Kessler Post author

      You should be able to daisy-chain the iMac in Target Display Mode, and have it be at the end of a line of Thunderbolt devices, so my advice to put it as the first is just a troubleshooting step and not necessarily a recommendation for all cases.

      You cannot daisy chain through the iMac’s thunderbolt ports. These ports belong to the iMac’s computer. When you enter Target Display mode, you logically disconnect the iMac’s monitor from its output, and switch it to accept an incoming DisplayPort signal to present on the monitor. The Thunderbolt connectivity of the port will still be managed by the iMac, and you should still be able to do things like Thunderbolt networking between the two systems.

  2. Donald Bruno

    Been reading your articles for a short time and find them really informative and easy to understand, I like them very much. You write about topics I don’t see often…been a Mac guy over 10 years but there is so much hidden and not discussed info ….sometimes just basic stuff …your articles are really good for me(hope other too)….not too technical that you have to be a geek to follow. Thanks for all you do,great work.

  3. Sphinn

    Please confirm before I buy another cable: I think I now know why I can’t get TDM to work with my setup based on the above article. Wanting to use 21.5-inch Mid 2010 iMac (w/Mini Display Port) as an external monitor for a 27-inch Late 2012 iMac (w/Thunderbolt Port). I tried a Mini Display to Mini Display cable and it didn’t work. From your post, a Thunderbolt to Thunderbolt cable should though, right? Only questioning because point #4 of this Apple article makes it look like it still might not based on the older iMac (not being supported?). http://support.apple.com/kb/ht3924#4
    Your posts are great!

  4. arex

    I’d like to add that even after resetting the iMac’s SMC, etc., if the switchover still doesn’t work, just try restarting the Macbook Pro. I wasted 20 mins of my life when the cause was actually the MBP itself.

  5. GaryC

    I have a new MBPro Retina and a late 2009 27 inch iMac. When I connect a miniDisplayPort cable between them (as per Apple’s instructions) and press CMD F2, the iMac screen goes black for about 10 seconds, then comes back on, but showing the iMac screen not the MBPro. The fact that it goes black shows the cable is working and the command is doing something, but not what it should. I use an external display at work, so the output of the MBPro is working. All OS and firmware is up to date (Mavericks on both). I have restarted both and attempted this several times without success. Is there another possible incompatibility?

    1. Martin Bonar

      Same problem. Then I opened System Preferences Displays and found a new option called ‘Arrangements.’ Checked the Mirror Display box and bingo! Set up is 2013 iMac 27 (Thunderbolt) to graphics crippled late 2009 iMac (MiniDisplayport) using MiniDisplayport to MiniDisplayport cable from MacLab.

      1. hawken

        That option will only come up if the broadcasting computer can sense the iMac as a second monitor. This is a different problem, the iMac’s screen is black and there are no arrangements options in the connected computer’s preferences (as it’s not sensing the iMac)

    2. hawken

      same problem. did you ever find a solution? I’ve tried with a macbook and pc, using miniDP and miniDP to DP cables. All I ever get a black screen.

      I’m on Mavericks.

  6. Våghals

    My problem is that if I switch to TDM the sound out changes to internal speakers. I have a Roland sound card that is connected to my speakers and before Yosemite it was no problem switching to TDM, the sound was still playing thru the sound card, but after upgrading to Yosemite it doesn’t work. After command F2 it set sound out to internal speakers. How do I report this bug to Apple?

  7. romero

    Hi! I’m using a Mac Pro Mid 2012 running Yosemite and I want to use a iMac Late 2009 running Yosemite. I plugged the mini display cable on both and did not work. I dont know if the cable is working or it cant be done between imac and mac pro. what should i do?
    thanks!

  8. goo gle isEvil

    Any idea on how to change the keyboard shortcut for switching? My system has worked fine for ages until I bought a radio shack wireless keyboard and cmd-F2 doesn’t work anymore. I see support forum posts for the same thing on Logitech keyboards too, so Apple did some undocumented magic that 3rd party makers didn’t know about.

    So, know a way to change that shortcut?

  9. Dave

    I have just purchased a late 2014 iMac retina display to hook up to my Macbook Pro retina (2012/13) I have a thunderbolt cable connected. Can i use it as a dual monitor?

  10. Brian

    Having trouble, hours in, no solution, help thx! 🙂

    2 Macs are connected with no acknowledgement. “Cmd+fn+F2” & “Cmd+F2” no response. In Displays Prefs panel, I need to hit “option” to see “Detect Displays” button. Click = no response

    Main: Late 2012 15inch Macbook Pro [Thunderbolt port]
    Display for TDM: Late 2009 27inch iMac [MiniDP port]
    Connection cord: MiniDP to HDMI + Adapter HDMI to MiniDP

    Forums & Apple support say the connection cord will work. Just dont daisy chain more than once.

    App store updates on both Macs are updated. Latest OSX10.10 on both.

    Help. €50 cord invested with no solution in sight.

    THANKS SO MUCH!

    Desperate for a 27″ i7 MacBook for FCP projects in Amsterdam,
    Brian

    1. hawken

      You’ll need to use a double male miniDP cable.

      I actually fixed my problem by replacing the cable with one I bought from Apple. Expensive but works fine, it seems they are very sensitive about the cable, not all MiniDP cables are equal. Converting to HDMI in the middle sounds unlikely to work.

      1. Brian

        Belkin cords are quality and Apple says it will work. Yet no response. I agree, the cord issue is the most likely culprit. Thanks for the advice, Im off to the Apple store! DOH!

      2. Brian

        Hit the Amsterdam Apple Store & you know what they told me? We dont carry those anymore, everythings on Thunderbolt and Lightning and THEY HAVE NO IDEA WHERE I CAN ONE. Thats after I hung out on the phone waiting for the person to pick up for 23mins. There goes the phone bill, so I walked in. BETTER SERVICE PEOPLE!
        So I found a male to male MDP 1.5m cord for €15 from the countries largest online cord store, we shall see tomorrow afternoon! THX AGAIN HAWKEN :)))))

  11. hawken

    Just want to say that I fixed this problem, not before tearing my hair out:

    Bought a cheap 2010 iMac, had the same problem as the Late 2009 iMac.

    It was the cable. Got a miniDP to MiniDP cable from Apple. Worked fine with mac laptops.

    My PC (geforce 970) doesn’t seem to work with the DP to miniDP. Tried a few cables and don’t get the correct signal.

    All in all it’s safe to say the iMac, it’s operating system etc is never the problem. Just the iMac is very sensitive as to what signal is being sent and on what cable.

    If in doubt do not go out and buy a replacement iMac (like I did!!), try some different cables first. PC is hit and miss, I’ll need to replace my geforce if I want to try again, and even then there are no assurances. It’s a dark well to fall down if this doesn’t work for you first time.

  12. Brian

    Update: Reset SMC on both. Held at same time “Shift+Ctrl+Option+Power” for 20 secs on Macbook = Power adapter LED flicker, restarted normal. Unplugged cord from iMac for 20secs, plugged back in, waited 5secs, restarted normal. No change.

  13. Jeff Van Minde

    I found, with the bluetooth apple keyboard, to turn off “Use F1, F2, etc..” under the System Preferences -> Keyboard menu. Once I did that cmd – F2 worked!

  14. Xeondxb

    i have 2011 mid IMAC 27inch and macbookpro 2013 late retina im trying to connect with thunderbolt cable after connecting both together on my imac and macbook pro thunderbolt port shows inactive but when i connect macbook air 2012 with my imac,it immediately become active and also i can see macbook air display on imac … can you help me what im missing ??

    1. Freakschnietz

      Do you found a solution yet? Because i have exactly the same issue and can’t find a reason why its not working.

      1. amir

        update thunderbolt firmware mine worked after updating. im searching old email if i’ll find that link i’ll post here.

      2. Freakschnietz

        i spoke a lot with the apple support and I even downgraded my system to “Yosemite” but nothing seems to work and even apple didn’t find a solution yet.

        @amir: it would be awesome if you find your mail

        1. Amir

          Whatever you are saying same things I did but nothing works for me… Then what I did I updated OSX on my both machines “os x el capitan”
          After that nothing changed then I called apple support that lady told me it won’t work. Gave her her reference apply website says it should work. I spoke to manager her name was ‘Michele Schramm’ she never gave up.… she really helped me.

          – Update os x el capitan
          – Update thunderbolt Link [ https://support.apple.com/kb/DL1407?locale=en_US ] on macbook pro I guess.
          – If it won’t work update on imac

          Update me if it work… Hope it will help other people also.

          Amir

          1. Nitefury

            This is awesome! I’ve been looking for a solution for hours! I have a Late 2013 iMac (thunderbolt) and an Early 2011 MBP (thunderbolt) and an Apple Thb-to-Thb cable and could not figure out why it wasn’t working. Tried everything in all the threads/support boards. This solved my issue. I only downgraded the driver on my MBP and it worked.

            Thank you!!!!

  15. Eric

    Trying to connect a Mid-2010 Mac Book Pro running 10.10.3 to an iMac to use as display, iMac is Mid 2011 running 10.10.2.
    iMac does nothing when I hit command F2 with or without fn held down. Reset controller (shut down unplugged for 15 seconds plugged in waited 5 seconds and restarted).
    Any ideas?

  16. Reed

    Hi,

    I’ve a Mid 2011 iMac and a Early 2015 Retina Macbook.

    I want my iMac to be the main i bought a thunderbolt cable and when i press Command + F2, nothing happen.

    Any suggestion?

    Thanks!

  17. David Baldry

    I am using late 2015 28″ IMac and 28″ Retina display connected by a thunderbolt cable. The Target display mode function works, but I can only play sound through on or the other and would like to play sound through both. Is that possible?

  18. Alison

    Trying to connect a mid 2014 retina macbook pro to a late 2013 imac. Have tried everything listed here and nothing works. My macbook pro doesn’t have any thunderbolt firmware installed so I can’t use the updater. Any other suggestions?

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