User profile for user: timpoitevin
timpoitevin Author
User level: Level 1
28 points

Target Display Mode not working 2019 iMac to 2013 iMac

I just brought home a brand new 2019 iMac, and I'm trying to use my Late 2013 iMac as a second monitor. Because the new iMac has USB-C, I have a USB-C-to-Thunderbolt adapter, and a Thunderbolt cord going into the old iMac. Pressing Command-F2 does not work (both with and without the Fn key). I have tried pressing it before login (at the login screen), and after I'm logged in. Tried it as a guest user as well. Nothing.


Is it the adapter that's getting in the way? I don't see any way to connect the two devices any other way. Little help, please?

Posted on Mar 29, 2019 6:28 PM

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User profile for user: ader42
ader42
User level: Level 1
8 points

Posted on May 11, 2019 8:38 AM

Okay, am replying in case anyone in the same situation finds this thread.

I seem to have got to the bottom of the problem.

My 2012 iMac has Mojave on it and runs pretty slowly.

So I figured maybe there is just too much going on - i.e. the 2012 iMac is too slow.

It seems that is why the TDM is so unreliable/flaky on my iMac.

If I am not logged in on the 2012 iMac, then it's not doing any work and importantly can still be put into Target Display Mode.

It seems to work flawlessly now, I have a 2019 iMac with 2012 iMac as a secondary monitor as long as the 2012 iMac does not have a user logged in.

I "guess" if the 2012 iMac was still running High Sierra or even Sierra then I wouldn't have had a problem.

So make sure your secondary iMac is logged out!

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User profile for user: darrylseanparsons
darrylseanparsons
User level: Level 1
4 points

Apr 30, 2019 3:25 PM in response to timpoitevin

Hi Tim, just to confirm, I also have a 2019 iMac i9 which I have successfully connected to a 2013 iMac as a second screen in Target Display mode. I used an Apple branded Thunderbolt 3 to Thunderbolt 2 adapter connected to a generic 'no-name brand' Thunderbolt 2 cable.


It can be a bit flakey with initial recognition for some reason though. I had to try a couple of times (pulling the cable out of the back of the 2013 iMac and putting it back in again) before it was recognised. I also had to reset the sound settings on the 2019 iMac back to 'internal speakers' afterwards as the 2019 iMac was a little confused by having the 2013 iMac attached and wasn't sure where to send audio. Other than those little niggles everything is working just fine.

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Target Display Mode not working 2019 iMac to 2013 iMac

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