Late 2015 iMac two external monitors

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Late 2015 iMac two external monitors

iMac (Retina 5K, 27-inch, Late 2015) with a 27" Thunderbolt display. According to specs, I can add another monitor. I have tried USB - HDMI adaptor, Thunderbolt 2 (MDP) to HDMI (actual Thunderbolt 2). MDP - HDMI. Nothing recognizes the third monitor. I have tried different HDMI cables, an external USB "dock". Nothing shows up. I have made sure the resolution is set properly and is not maxing things out.

What am I missing? Any help would be greatly appreciated.

iMac 27″, macOS 10.14

Posted on Sep 17, 2021 7:40 PM

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Answer 1

Top-ranking reply

Malcolm J. Rayfield

Level 7

23,059 points

Sep 19, 2021 11:48 AM in response to RevRemM

You should have the Thunderbolt display plugged into one of the computer's Thunderbolt ports and a Mini DisplayPort to HDMI adapter in the computer's other Thunderbolt port. You can't use the port on the back of the Thunderbolt display for the HDMI adapter. (It can be used for a second Thunderbolt display, though).

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Answer 2

Sep 17, 2021 8:44 PM in response to RevRemM

What is the third monitor?

iMac (Retina 5K, 27-inch, Late 2015) - Technical Specifications

"Simultaneously supports full native resolution on the built-in display and up to two 4096-by-2160 external displays or one 5120-by-2880 dual-cable external display"

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Answer 3

RevRemM Author

Level 1

5 points

Sep 18, 2021 12:41 PM in response to Malcolm J. Rayfield

Thanks for chiming in to help. This has been a frustrating.

I am only trying to add a Samsung 21" LED using an HDMI input.

I am also considering installing (later date) another 27" Thunderbolt display.

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Late 2015 iMac two external monitors

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