2018 MacBook Pro Target Display Mode Not Working

Pennock,

Nice to hear from someone in the cyber yonder.

Let's see what they say tomorrow. I can't really hang around for X amount of days/weeks/months while Apple may or may not fix this... who knows, maybe the tech is even impossible to implement? Or they want to serve a death warrant to display ports much like firewire seems to have now been ditched? While I would prefer not to sell my iMac and not buy a Dell XXX or ASUS ZZZ to do the same task it may be more prudent to go this way and get to work properly. (Or borrow a spare HDMI monitor for a while).

I'm having the exact same problem, I contacted customer support and I have yet to receive an answer on this issue. I even provided a video of the issues that I'm having while using target display from new 2018 MacBook pro to my 2011 iMac. Maybe their recommendation will be for me to buy a new iMac? 😠

"Maybe their recommendation will be for me to buy a new iMac?" - I believe since 2014 the new iMacs do not support Target Display Mode, so they will not suggest that you purchase a new iMac maybe a new monitor.

They should have it resolved soon

Same issue. I was using Target Display Mode (TDM) with my MBAir to my 27-inch, Late 2012 iMac, and it worked fine. I bought a 13-inch 2018 MBP I was excited to use with my iMac in TDM to replace my MBAir. I plugged in my new MBP and just got a black screen. After many trips to Best Buy thinking it might be a faulty cord or adaptor, I ended up with what I think is the simplest solution - an Apple branded Thunderbolt II to USB-C adaptor and a Apple branded Thunderbolt II cable. With this set up the best results I get is an intermittent scrammed image fluxing between clear and scrammed (every 30 seconds or so). Sometimes if I wait long enough it will clear and the screen will look fine until I exit out, but when I boot back into TDM it starts the scrambling all over again. If the screen goes black and stays black I will need to exit out of TDM and then wait until the next day to attempt to try to get it to work again.

I called Apple Support they worked with me for two weeks and kept escalating my problem to higher and higher. Finally they said it would be a firmware update for both the iMac and the MBP and to look for it in upcoming software updates.

As of today Sept 19, 2018 there has been two software updates for the MBP and one for the iMac but nothing addressing the TDM issue.

I will be following this post to see what others say.

After tedium with Apple on-phone support it was clear this was going no where fast.

FIXED:

So, for a busy person, I spent way too long researching dongles and found a Sicotool USB-C dongle that has a mini display port in it - worth a try I say. And look at that.... At the same price as a Apple T3-T2 Adapter, this dongle does a marvellous job at getting a monitor signal from one of my 2018 15" MBP's T3 port to my late-2009 iMac's mini display port. I don't even have to faff with Target mode, it instantly finds it and got dual screen. The image is also perfect, better than what I had with my 2012 MBP (i.e., no faint ghosting etc).

Well done random Chinese dongle manufacturer - you've done what Apple can't do!

This thread is for Target Display Mode NOT mini display port out, researcher_ash...

Most of the people on this thread are interested in using TDM on their 2010 -> 2013 iMacs. I think before 2010 and after 2013 they do not have TDM. I would only go about what researcher_ash says if you're having the exact issue with the same setup that he has. I'm following up on this thread as I do not want people thinking this will solve their issue connecting to 2010 -> 2013 iMacs.

If I'm wrong about this please follow up as I would love to resolve this ASAP and I'm still in my return window for the Apple Thunderbolt 3 -> 2 adapter. But from what I have read and research that I have done it will not.

Possible work-around for most users here, is to launder the signal provided by your 2018 MacBook Pro through a ThunderBolt Hub. This seems to re-drive the signal, and make it conform in a way that the iMac can accept without issues.

Hi. Yes ok. I had thought my iMac, the late-2009 27", was automatically going into TMD when a mini Display feed was stuck into it. But if it's not then sorry to get anyone's hopes up. I wonder what it is then other than a TMD process?

researcher_ash wrote:

I had thought my iMac, the late-2009 27", was automatically going into TMD when a mini Display feed was stuck into it.

It is using Target Display Mode, but via Mini DisplayPort, not Thunderbolt (which wasn't on the 2009 iMac). The flicker problem is only with Thunderbolt using the 2018 MacPro,

As I posted previously I have the same issue with a new 2018 13" MBP and a Mid-2011 iMac (which worked perfectly with my mid-2015 15" MBP. I could not wait any longer for Apple to fix so I went ahead as others have suggested and purchased a hub. An unfortunately expensive solution but A SOLUTION. I can confirm as others have that it does indeed work. I purchased the CalDigit TS3 Plus+ plugged in using the Apple TB3 to TB2 adapter and I'm up and running. It stung a little to have to shell out more money on top of the already large expense of a new laptop but the bonus upside is that I now have ports for any peripherals that don't have TB3.

Exactly the same problem for me. I've spent hours with technical support without any success.

Tried different 3rd party adapters but still no luck.

Apple, please sort out the problem.

MacBook Pro 2018 15" i9 + iMac 28" mid 2011 with i5

thanks,

Waldemar

Malcolm J. Rayfield wrote:

It is using Target Display Mode, but via Mini DisplayPort, not Thunderbolt (which wasn't on the 2009 iMac). The flicker problem is only with Thunderbolt using the 2018 MacPro,

But technically, should't it work? Isn't thunderbolt supossed to take a minidisplay cable?

I'm considering it as a cheaper solution to connect my MBP 2018 to my thunderbolt iMac mid 2011.

Opinions?

Thunderbolt iMacs require a Thunderbolt cable for Target Display Mode. A Thunderbolt port (except that on the back of a Thunderbolt display) can be used for video output with a Mini DisplayPort cable, but video input requires a Thunderbolt cable.

I have the same issue.
Macbook Pro mid 2018 i9 32Gb 15" (OSX 10.14)
iMac mid 2011 21.5" with thunderbolt connection (OSX 10.13.6)

Apple thunderbolt 3 to 2 apple original.
I can't use my iMac as a second display

From my MacBook Pro late 2013 to iMac mid 2011 it's working fine (so the thunderbolt cable is OK)

macOS Mojave is out. I downloaded it on both my MacBook Pro and iMac with a faint hope there might be a fix. Not surprised but saddened that there is still no fix. It is obvious this is not a priority for apple, I don't even think anyone is working on it. Prove me wrong Apple, please fix this.