new M1 iMac will not recognize external Thunderbolt Display

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Level 1

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new M1 iMac will not recognize external Thunderbolt Display

I have a new M1 iMac (arrived two weeks ago) and would like to use my 27-inch Thunderbolt Display as a second monitor. I purchased Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter to connect them but the iMac does not recognize the Thunderbolt Display. The "Thunderbolt/USB4 Device Tree" in the iMac's System Information shows both USB4 Bus 0 and USB4 Bus 1 but reports "No device connected" to either Bus. I know that the Thunderbolt Display is working because it will come on when plugged into the Thunderbolt port on my 2013 MacBook Air.

Posted on Jul 25, 2021 2:08 PM

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Answer 1

Jul 27, 2021 6:42 AM in response to sandcarver

Sorry if this is too simple, but if you have the 4 port iMac, are you plugging into the Thunderbolt ports and not the USB-C ports? They are not interchangeable.

(I found this out with my Thnderbolt3-Thunderbolt-2 adapter for my firewire camera. I had it plugged into the USB-C, and kept getting a notice that USB-C does not support Thunderbolt devices. I finally read the notice, went Doh!, plugged into the Thunderbolt port and everything was fine.)

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Answer 2

tbirdvet

Level 6

17,731 points

Jul 27, 2021 8:30 AM in response to sandcarver

I just wanted to be sure you were not using an extension cable from adapter to Mac. I guess it is possible that the adapter is bad like you stated. Can you exchange for another one?

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Answer 3

tbirdvet

Level 6

17,731 points

Jul 25, 2021 2:26 PM in response to sandcarver

I assume you are connecting directly and not through a hub?

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Answer 4

Jul 25, 2021 2:46 PM in response to sandcarver

-deleted irrelevant-

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Answer 5

sandcarver Author

Level 1

6 points

Jul 25, 2021 2:48 PM in response to tbirdvet

Yes. Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter plugged into Thunderbolt port on back of computer and Thunderbolt cable from Thunderbolt Display plugged into adapter.

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Answer 6

tbirdvet

Level 6

17,731 points

Jul 26, 2021 4:59 PM in response to sandcarver

Not sure why it does not work. I have a MBA M1 that I connect to my TB display and it works great useing the same adapter. Is the cable from the adapter to your Mac a TB3 cable?

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Answer 7

sandcarver Author

Level 1

6 points

Jul 27, 2021 6:14 PM in response to Keith Barkley

It is a 4-port iMac and, yes, I have plugged it into both of the Thunderbolt ports--which are clearly marked--without success.

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Answer 8

sandcarver Author

Level 1

6 points

Jul 27, 2021 6:15 PM in response to tbirdvet

No extension cable and since I just bought the adapter a few days ago I presume that it can be exchanged for another one. I also bought 3 years of AppleCare so perhaps they can help.

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Answer 9

sandcarver Author

Level 1

6 points

Jul 26, 2021 8:30 PM in response to tbirdvet

The Thunderbolt 3 (USB-C) to Thunderbolt Adapter (https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter?fnode=1292468ac936bc0d44bbc9f982bb66ba04e0addea3c4e15cb0022574356a20748f99a82addd5e261514ace9baa15c984a42e539a7b2aeeefffcb866945249f25437f7b8d8d54c976b9fb4e86cfb9791d04bd8840382acbb355e9b088a0fb0616) is plugged into either of the Thunderbolt ports on the M1 iMac and the Thunderbolt cable that is hard-wired into the 27-in Thunderbolt Display is plugged into the other end of the Adapter.

I've plugged an external drive into the Thunderbolt ports of the M1 iMac (using an Syntech USB C to USB adapter) and the computer is able to read and write to the external drive. That's the only way I've been able to test the ports. And as mentioned in my initial post the Thunderbolt Display seems to be working. So I'm thinking that the adapter I purchased from Apple must be bad.

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new M1 iMac will not recognize external Thunderbolt Display

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