Target Display Mode - Stopped Working

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Level 1

8 points

Target Display Mode - Stopped Working

I have a late 2013 27" iMac and a 2019 MacBook Pro...

Up until a couple of days ago TDM worked fine for me through the usual cmd-f2 shortcut, and then all of a sudden it stopped working.

I did some searching and it seemed likely that upgrading my iMac to Catalina was the problem, so I reset the iMac and reinstalled High Sierra 10.13.6. The MacBook Pro is running Catalina 10.15.6

I've tried every recommendation I have come across in trying to solve this (checked keyboard settings, restarting both machines etc, resetting nvram or something like that)... and nothing has worked.

Any more ideas on how to fix this?

iMac 27″, macOS 10.13

Posted on Jul 21, 2020 9:23 AM

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Answer 1

BDAqua

Level 10

250,253 points

Jul 21, 2020 10:01 AM in response to sil693

Yeah, High Sierra on the Target Mac is supposed to be the highest that works.

Have you done a PRAM reset, CMD+Option+p+r...

http://support.apple.com/kb/HT1379

In fact, do 3 in a row, takes a bit of time.

Intel-based Macs: Resetting the System Management Controller (SMC)...

http://support.apple.com/kb/HT3964

https://support.apple.com/en-us/HT201295

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Answer 2

BDAqua

Level 10

250,253 points

Aug 6, 2020 8:18 AM in response to sil693

Starting to sound like a bad cable or port.

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Answer 3

sil693 Author

Level 1

8 points

Aug 7, 2020 2:36 AM in response to BDAqua

I've just been trying again and after maybe an hour of having the machines connected the "connecter / adapter' which plugs into the MacBook is HOT. Given the cost I'm reluctant to replace it in case it doesn't resolve the issue... although I now feel like I'm looking at an iMac which I'm not going to use!

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Answer 4

sil693 Author

Level 1

8 points

Aug 6, 2020 3:13 AM in response to BDAqua

Unfortunately not...

I did the PRAM reset 5 or 6 times until I heard the startup sound twice, so I'm confident I did that part right. I'm still not able to use the cmd-f2 function though.

Previous to it not working - occasionally when I pressed cmd-f2 the target Mac screen would go black, and it'd take a little bit of messing about with wires etc. before it actually extended my screen correctly - but now I don't even get that. The cmd-f2 function has no effect whatsoever.

It's very frustrating!

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