iMac Pro 2011 iMac upgrade SSD and CPU, cannot use Target Display Mode.

[mikko127]

Hi all,

I have a Target Display Mode question. I have the 2011 iMac that originally had HDD and i5 cpu. Then about two years ago, I took the liberty to upgrade the HDD to a SSD, and change the cpu from i5 to i7 2600s. Just recently I got a 2017 iMac and would like to use the old 2011 iMac in target display mode but it wouldn't work. I checked the spec, I am using thunderbolt to thunderbolt cable, the 2011 iMac is running 10.13.6 (High Sierra) and the 2017 iMac is on 10.14.6 (Mojave). Don't know if the Target Display Mode won't work is because I change the HDD to an SSD or is it because of the the cpu upgrade. Or perhaps I got the wrong thunderbolt cable, although I did try the cable at a friend's place and it did work with his iMac and his MBP.
Help anyone?

 

[tgaillar]

Try to boot your 2017 iMac with 10.13 High Sierra (external disk or add a 10.13 partition) and see if TDM over Thunderbolt works (I guess it should). If it does, then Mojave on the 2017 iMac is likely the culprit...

 

[chscag]

I have a Target Display Mode question. I have the 2011 iMac that originally had HDD and i5 cpu. Then about two years ago, I took the liberty to upgrade the HDD to a SSD, and change the cpu from i5 to i7 2600s. Just recently I got a 2017 iMac and would like to use the old 2011 iMac in target display mode but it wouldn't work.

Target Display mode is not supported for Retina iMacs which is why it doesn't work. A 2017 iMac has a retina screen. You can search for the Apple support article which gives the reason it does not work.

 

[mikko127]

Thanks for the replys. This past week I borrow my friend's non-upgraded 2011 iMac that still ran on Maverick OS (10.9) and had the original HDD and CPU. And sure enough, the Target Display mode worked flawlessly on his non-upgraded 2011 iMac (Maverick) and my 2017 iMac (Mojave). Next I tested out with my upgraded 2011 iMac (High Sierra) and his non-upgraded 2011 iMac (Maverick) and that worked too. So that leads me thinking Target Display mode works on his non-upgraded 2011 iMac (Maverick) because it is not upgraded. I never tried the Target Display mode before the upgrade so I don't know if that is the cause of the problem. Any suggestions? I just don’t want to let my 2011 iMac go to waste.