iMac Target Display Mode not working - 10.14 2009 27"

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Level 1

20 points

iMac Target Display Mode not working - 10.14 2009 27"

Using

iMac 2009 i7 High Sierra 10.13
MacBook Pro 15" 2014 Big Sur 11.2.3

Problem:

So, I have struggled like many on these forums to solve why my iMac is no longer allowing Command-F2 to enter Target Display mode, which I think was genius by Apple. I have ruled out nearly all the solutions offered across the forums.....such as PRAM, SMC, safe mode, logout, and even installed a fresh copy of High Sierra - Nothing.

Then it occurred to me, I was using a Thunderbolt 2 wire, which is DisplayPort compatible. However, the iMac 2009 I'm using only supports DisplayPort. I got out my old DisplayPort cable, plugged it in, and everything works great! I thought I have used Thunderbolt 2 cables before, but I won't try them again.

Solution: Use Display Port cable between machines.

What doesn't work: Thunderbolt 2 cable. While TB2 cables are DisplayPort capable, apparently they are IF the computers support Thunderbolt 2 on both ends.

Posted on Jun 18, 2021 6:48 AM

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Answer 1

Jun 18, 2021 7:30 AM in response to Clarknet

Your MacBook Pro 15" running Big Sur does not support target display mode.

Apple has not supported Target Display mode out of the box on any iMac since 2014, nor on any macOS newer than 10.13 High Sierra.

Only a small handful of iMacs were ever supported to target display mode:

"Note: Target Display Mode isn’t supported on iMac models with Retina display. Only iMac (27-inch, Late 2009), iMac (27-inch, Mid 2010), and iMac (Mid 2011 to Mid 2014) support Target Display Mode.”

For the intended target (the iMac being used AS a display):

"Target display mode requires macOS High Sierra or earlier. It does not work with macOS Mojave or later.“

Use your iMac as a display with target display mode - Apple Support

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Answer 2

Clarknet Author

Level 1

20 points

Jun 18, 2021 8:21 AM in response to D.I. Johnson

D.J. - Thanks for replying. There are many many users out there holding onto older iMacs and MacBooks and they would like to have solutions like I've posted. That is why I posted the years of the macs, and explicitly the cables I am using, for clarity. There are far more users on older Apple machines capable of using Target Display than there are users using non-compatible Target Display machines. The newer machines, maybe in the last year or two.

This needs to be addressed for others clarity: "Your MacBook Pro 15" running Big Sur does not support target display mode." -

My MacBook Pro 2014 works great with my iMacs in Target Display mode. Running Big Sur too!

If someone looks at my post, they will be looking for solutions to keep aging Macs alive and useful. A user with an M1 Macbook won't be misled if they read my post. Nothing fits an M1 user that I wrote about.

There are many many iMac's out there that people continue to use, and would like to continue to do so. And more that use their aging iMacs as second monitors, especially MacBook users. The total number of users using iMacs, and MacBooks, that support Target Display mode is a very very large user base.

Just trying to help others.

D.I. Johnson wrote:

Your MacBook Pro 15" running Big Sur does not support target display mode.

Apple has not supported Target Display mode out of the box on any iMac since 2014, nor on any macOS newer than 10.13 High Sierra.

Only a small handful of iMacs were ever supported to target display mode:

"Note: Target Display Mode isn’t supported on iMac models with Retina display. Only iMac (27-inch, Late 2009), iMac (27-inch, Mid 2010), and iMac (Mid 2011 to Mid 2014) support Target Display Mode.”

For the intended target (the iMac being used AS a display):

"Target display mode requires macOS High Sierra or earlier. It does not work with macOS Mojave or later.“

Use your iMac as a display with target display mode - Apple Support

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Answer 3

Old Toad

Level 10

216,500 points

Jun 18, 2021 10:05 AM in response to Clarknet

Clarknet:

You should mark your original post to this topic as solved so others will know that there is a solution included in the topic.

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Answer 4

Jun 18, 2021 8:43 AM in response to Clarknet

Clarknet, thank you for clarifying this. I owe you an apology. Due to my caffeine imbalance this morning I misread your original post.

I did not realize you were specifying that you had a fix for the issue - use a DisplayPort cable.

That's awesome! A lot of people will be happy to know about this. Thank you!

And, sorry. 🙂

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iMac Target Display Mode not working - 10.14 2009 27"

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