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I have two external monitors (both are Sanyo TVs). My Macbook Pro has one Thunderbolt. I purchased a Mini DisplayPort to Dual HDMI Adapter. The adapter is connected to the Mini Display port and to a USB. I have two HDMI cables, each connected to their own HDMI port in the adapter. My problem: The laptop works just fine independently; however, the two external monitors mirror each other. I have tried clicking on Display and clicking on Detect Displays but it does not detect the 3rd monitor or if it does, I am unable to make it work independent of the 2nd monitor - Help, Please!

marked as duplicate by Allan, LH16, JMY1000, fsb, Mark Feb 19 '18 at 10:00

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Are you able to confirm that your MiniDisplay port to 2x HDMI cable supports two separate outputs and not just mirroring of the output?

If you go to System Preferences : Displays : Arrangement can you see the two monitors?

Can you uncheck the box the says “Mirror Display”?

If you don’t see the two monitors, I’d guess that the adapter is an HDMI splitter and does not support two Independant desktops.

  • I only see two monitors, not three.. I can check and uncheck the Mirror Display. – Galtin Feb 19 '18 at 3:11
  • Do yo have specs or a user manual for your adapter? Can you confirm that it is intended to output two distinct displays and not just act as a splitter? – Tukanuk Feb 19 '18 at 3:15
  • Not sure what specs you are looking for? It is a j5create JDA156. – Galtin Feb 19 '18 at 16:48
  • See the specs page. The adapter does not support what you are trying to do on MacOS. Extended mode looks limited to Microsoft Surface Pro. – Tukanuk Feb 19 '18 at 19:32
  • Hello: I now have a Matrox DualHead2Go external multi-display adapter. I have a Macbook Pro Late 2011 13". All three monitors are working, somewhat (2 external Sanyo 32" TVs and my laptop.) The MBP shows the menu and docking station perfectly and independently; however, the 2 external monitors are being treated as an extension of each other, though I can have 3 separate Excel spreadsheets opened - 1 on each monitor - The Built-in Display of the MBP only shows two displays. Is there a way to have all 3 monitors work independently of each other? Thank you, Wen – Galtin Mar 11 '18 at 23:00

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