Using an older Imac (2013) for a second monitor on new Imac (2020)

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Using an older Imac (2013) for a second monitor on new Imac (2020)

I have followed every instruction that Apple has about connecting my older Imac, (late 2013) 21.5 inch to my 27" 2020 Imac. I have the Thunderbolt cable 3.3 ft, as well as the newest adapter which is the USB-C allowing the connection from the Thunderbolt 2 cable to the new Imac. I restarted both machines, and did the Command+F2, nothing. The screen is supposed to go black and come back on as a monitor only. It does not. The older Imac is running Catalina, the new is running Big Sur 11.2.1. What am I doing wrong??? I really need this second monitor. I also tried using my older Cinema screen, that also will not work. I have the original keyboard for both machines. Any other suggestions??? Thank you!

Posted on Feb 25, 2021 1:04 PM

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Answer 1

Top-ranking reply

Limnos

Level 10

418,627 points

Feb 25, 2021 1:09 PM in response to Valerie Mcmillen

Hello valerie,

I think the issue may be Big Sur. Using iMacs in Target Display Mode is no longer supported. Read this topic for a 2021 perspective on this: https://discussions.apple.com/thread/252271436?answerId=254300142022#254300142022

and this 2021 post by Allan Jones about software limitations:

https://discussions.apple.com/thread/252344497?answerId=254428494022#254428494022

Here's Apple's original document about that but as you can see, it has been "archived" which is what they do with something that is no longer supported under newer systems and equipment.

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

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Answer 2

rkaufmann87

Level 10

143,892 points

Feb 25, 2021 1:22 PM in response to Valerie Mcmillen

Bottom line is TDM will not work with a 2020 imac. Apple killed off TDM back in 2015 and the final nail was put in the coffin when the 2020 iMacs came out. Return the expensive cables you bought and then use that money towards buying an external display.

Please remember iMacs were never designed to be external displays for other devices, it was a fluke TDM worked many years ago. Using an external display is MUCH easier to setup and much more reliable than TDM ever was. In addition external displays are relatively inexpensive, a good quality one can be purchased for about $130 at Costco.com.

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Using an older Imac (2013) for a second monitor on new Imac (2020)

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