Target Display Mode MacBook Pro 2018 to iMac Mid 2011

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Target Display Mode MacBook Pro 2018 to iMac Mid 2011

I'm trying to use a 21.5-inch Mid 2011 iMac (High Sierra 10.13.4) as an extended display for a new 15-inch MacBook Pro 2018 (Mojave 10.14).

I am connecting from the MacBook Pro using a Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter together with a regular Thunderbolt cable.

The 21.5-inch iMac does absolutely nothing when I press command + F2 (to enter Target Display Mode).

I've checked with Keyboard Viewer and the iMac is definitely recognising that I'm pressing Cmd+F2, but it seems to ignore the keystroke completely.

Any ideas?

Thanks

Andy

Posted on Oct 31, 2018 5:32 PM

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Answer 1

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Andy Mees Author

Level 6

12,610 points

Nov 1, 2018 5:21 PM in response to SeaPapp

Mystery solved.

It seems that despite recognising the keystrokes from my old Apple Extended keyboard (without 'Fn' key, and thus no "Use F1, F2 etc..." option in Keyboard System Preferences) it was indeed ignoring the Cmd+F2 command. I suspect that the OS default setting of "Use F1, F2 etc..." was overriding the command even tho the option to change it wasn't available. I switched the keyboard over to an Apple Bluetooth keyboard, the "Use F1, F2" option became available ... which allowed me to switch it off... and hey presto, the TDM toggle works.

Unfortunately, when I turned TDM on, the screen on both iMac and MacBook started blinking and glitching like something possessed... luckily a quick update to Mojave 10.14.1 fixed that too. All is well.

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Answer 2

SeaPapp

Level 7

26,486 points

Nov 1, 2018 5:21 PM in response to Andy Mees

In Keyboard System Preferences, if the checkbox is enabled for "Use all F1, F2, etc. keys as standard function keys," the key combination changes to Command-Fn-F2.

Use your iMac as a display with Target Display Mode - Apple Support

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Answer 3

Andy Mees Author

Level 6

12,610 points

Oct 31, 2018 8:05 PM in response to Andy Mees

I suspected it may be a problem with either my USB-C adapter or the Thunderbolt cable, but I've just checked the adapter with a Lacie Rugged Thunderbolt hard drive and that is seen and functions perfectly ... so its not the adapter.

I've also just checked my Thunderbolt cable with a Matrox DS1 Thunderbolt dock (via the same Thunderbolt 3 to Thunderbolt 2 adapter) and that is also seen and is working just fine... so it's not the cable.

The mystery continues. :-(

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Target Display Mode MacBook Pro 2018 to iMac Mid 2011

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