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User profile for user: EVways
EVways Author
User level: Level 1
11 points

Target Display Mode (TDM) stopped working on a late 2012 iMac

I have two late 2012 Imacs, one has been upgraded with an SSD - thi is my primary machine so lets call this Imac 1, the other one I now wish to use as a monitor lets call this Imac 2


Imac 1 is running 10.15.3

Imac 2 is running 10.10.5


TDM was working fine on Imac 2 when running high sierra. My issues started when I upgraded this machine to Catalina -it was then TDM stopped functioning -as a fix IMac 2 has been completly wiped and taken back to its 'out of the box' state and now is running El Capitan


TDM works fine from Imac 1 when i hit cmd F2 BUT cmd F2 fails to activate TDM on Imac2, the screen does not go black -nothing happens.


I have purchased a new apple thunderbolt to thunderbolt cable as some say this could be the issue -no luck!


I have tried many suggested fixes including cmd+fn+F2


The system report on both machines shows the Thunderbolt cable is connected


Any suggestions on how to fix would be highly appreciated!





The

iMac 27", OS X 10.10

Posted on Apr 29, 2020 12:03 AM

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User profile for user: SeaPapp
SeaPapp
User level: Level 7
26,486 points

Posted on Apr 29, 2020 2:55 AM

Use your iMac as a display with target display mode - Apple Support

If target display mode doesn't work

If your iMac doesn't show the desktop of your other Mac, try these steps first:

  1. Restart your iMac.
  2. Restart the other Mac.
  3. Unplug the Thunderbolt or Mini DisplayPort cable from the other Mac, then plug it back in.
  4. Press Command-F2 on the iMac.

If that doesn't work, try these other solutions:

  • If you're currently logged in to the iMac that you want to use as a display, choose Apple menu  > Log Out to return to the login window. Then press Command-F2 again.
  • Choose Apple menu  > System Preferences, then click Keyboard. If ”Use F1, F2, etc. keys as standard function keys” is selected, target display mode uses Command-Fn-F2 instead of Command-F2. It might also help to use the keyboard that came with your iMac. Some third-party keyboards and older Apple keyboards don't support target display mode. 
  • Make sure that your iMac is using macOS High Sierra 10.13.6 or earlier. You can't use target display mode with later versions of macOS, or with Boot Camp and Windows.



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Question marked as Top-ranking reply
User profile for user: SeaPapp
SeaPapp
User level: Level 7
26,486 points

Apr 29, 2020 2:55 AM in response to EVways

Use your iMac as a display with target display mode - Apple Support

If target display mode doesn't work

If your iMac doesn't show the desktop of your other Mac, try these steps first:

  1. Restart your iMac.
  2. Restart the other Mac.
  3. Unplug the Thunderbolt or Mini DisplayPort cable from the other Mac, then plug it back in.
  4. Press Command-F2 on the iMac.

If that doesn't work, try these other solutions:

  • If you're currently logged in to the iMac that you want to use as a display, choose Apple menu  > Log Out to return to the login window. Then press Command-F2 again.
  • Choose Apple menu  > System Preferences, then click Keyboard. If ”Use F1, F2, etc. keys as standard function keys” is selected, target display mode uses Command-Fn-F2 instead of Command-F2. It might also help to use the keyboard that came with your iMac. Some third-party keyboards and older Apple keyboards don't support target display mode. 
  • Make sure that your iMac is using macOS High Sierra 10.13.6 or earlier. You can't use target display mode with later versions of macOS, or with Boot Camp and Windows.



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Target Display Mode (TDM) stopped working on a late 2012 iMac

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