Target Display Mode not working 2019 iMac to 2013 iMac

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

You should be using this adapter

Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple

and this cable

Apple Thunderbolt Cable (0.5 m) - White - Apple

@tim/@malcolm, unless I'm mistaken, newer iMac models can't be used with Target Display Mode. See the note here Use your iMac as a display with Target Display Mode - Apple Support (also copied below):

iMac (Retina 5K, 27-inch, Late 2014) and later iMac models can't be used as Target Display Mode displays.

It's quite possible the new 2019 iMac is capable of doing it and the documentation simply is not up to date, but I hadn't heard that that would be the case. If you do manage to get it to work, please let us know. I would drop $3k right now for a new iMac if I could get TDM back.

"I have a Mini DisplayPort to Mini DisplayPort cable, which plugs into the old Mac and into an Apple thunderbolt 2 to thunderbolt 3 adaptor into the new Mac with no luck."

That adapter does not work for Mini DisplayPort.

About the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple Support

"This adapter is not compatible with displays that use DisplayPort or Mini DisplayPort"

If your 2009 iMac is 27" you can use a USB-C to Mini DisplayPort cable.

https://www.startech.com/AV/display-and-video-adapters/usb-c-video-adapters/usb-c-mini-displayport-cable-6ft~CDP2MDPMM6B

Look in the Thunderbolt section of System Information (Option-click at the top-left of the screen) on both computers. Each should see the other computer if the Thunderbolt cable and adapter are working.

Hi there!

I have an ongoing open case with Apple about this issue. I have a late 2009 iMac and a 2019 imac and I’m attempting this same thing.

I have a Mini DisplayPort to Mini DisplayPort cable, which plugs into the old Mac and into an Apple thunderbolt 2 to thunderbolt 3 adaptor into the new Mac with no luck. Apple have been investigating and made me try multiple things. They did a remote capture and can see that the new Mac is not detecting the old Mac. They believe it may be the cord. I haven’t tried a thunderbolt cord yet but I might try what you said.

Can you update me and tell me if it continues to work?

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.

SOLUTION! Don’t listen to apple’s advice, i was told to get an Apple brand thunderbolt 3 to thunderbolt 2 adaptor and a Mini DisplayPort cable to connect my late 2009 and current iMac for target display mode, they got me to try EVERYTHING. Turns out the blatantly obvious is why it didn’t work, Mini DisplayPort and thunderbolt 2 are not the same thing. Go to officeworks, get a thunderbolt 3 to Mini DisplayPort port adaptor for about $30 and use a Mini DisplayPort cable and your set! I plugged in and installed connected the two without pressing or doing anything.

Nice one Grayfox. That solution should work for all iMacs from 2009 to late 2012 as well. In a few months you probably won't be able to get a 2009 - 2013 iMac for love or money as they all get snapped up and repurposed as cheap secondary displays.

There's been a lot of commentary on the net complaining about Apple not updating the form factor on the 2019 iMac, but I'm currently sitting at a desk with a new 2019 iMac, a 2013 iMac and a 2012 iMac all side by side - the older iMacs running as secondary screens while their SSD's and CPU's are hard at work as part of a networked render-farm for 3D applications and After Effects. Next to the iMacs is a stack of four 2012 Mac Minis (also part of the render-farm) And because they all share the same form factor it looks beautiful. The old tech and the new tech working together for the greater good and sharing a visual harmony that makes them pleasing to the eye. So I'm pleased that Target Display is functional.

If I had seven different computers on my desk, all with completely different form factors it would look like an unholy mess.

Totally agreed on the form factor. I have my two side by side and all is well in the world because it’s symetrical and balanced, I would have been disappointed if it was updated and I had two different looking Macs. I have to look into what you are talking about and using the computing power as a joined network. I do movie editing so if there is a way to ‘farm’ the power of the older Mac for a greater cause that sounds good.

So glad I was able to get target display mode to work so I have more room to move around with all the editing tools and windows I have open at once. I have communicated my solution to Apple so I hope they can start spreading the correct advice and hopefully the techs at Apple can finally understand that Mini DisplayPort and thunderbolt are not the same thing even though they have identical physical inputs. ****, it even says on the adaptor box that Mini DisplayPort is not compatible.

"Go to Officeworks, get a Thunderbolt 3 to Mini DisplayPort port adaptor for about $30"

That's actually a USB-C to Mini DisplayPort adapter.

https://www.officeworks.com.au/shop/officeworks/p/comsol-usb-c-to-mini-displayport-adaptor-cocmmdf

I recently got a 2019 iMac too. Already had a Thunderbolt cable from connecting my 2014 iMac to my Late 2013 MacBook Pro so got the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter. Want to use a 2012 iMac as a second display.

At first all I got was a black screen on the 2012 iMac. Then I pressed option to "detect displays" and it worked.

However, later in the day my screen-saver kicked in and turned it off. I have been unable to get it to work again :(

I had it working once so the cables must be correct?

The 2019 iMac does detect the display as it shows both in "About this mac" > "Displays".

I can also change the "arrangement" in system preferences.

If I use the Thunderbolt cable between my Late 2013 MBP and the 2012 iMac it works fine straight away.

Tried restarts and "Detect Displays" over and over to no avail.

Tried SMC and PRAM resets too.

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!