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I have a MacBook Pro 2017, running High Sierra 10.13.3 (17D102) connected to a ThinkPad USB-C Dock, and two Dell U2412M screens attached to the dock, one by HDMI to Thunderbolt and the other by DisplayPort to DisplayPort.

OSX successfully detects both screens, as seen in Displays dialog,

Displays

But for some reasons, most of the time, the secondary screen stays turned off. It might, or might not, wake up anytime during my work on the computer. The behavior of it is pretty inconsistent.

I tried changing the connections to every possible variation, DisplayPorts only, switching ports, literally everything, but the behavior of the second screen keeps being unstable.

What am I missing? Why is the second screen mistreats me like that?

  • I would suspect that this dock can't drive two monitors as you expect. From the first bullet point in the link you provided: Enjoy a vivid video experience with an UHD display (4k@30Hz) or take multi-tasking with two FHD displays (1080p). You get either 1 a 4K or 2 at FHD. This is probably something you need to address with Lenovo. – Allan Feb 22 '18 at 10:32
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    I'm voting to close this question as off-topic because Customer Support questions are outside the scope of what can be asked here as defined in the Help Center – Allan Feb 22 '18 at 10:35
  • @Allan, the screenshot I attached is showing that I am not using 4K resolution on both screens, therefore it should work. Moreover, it works perfectly for a colleague of mine. – Quaker Feb 22 '18 at 11:34
  • Wouldn't 1080p (FD) resolution be 1920x1080 and not 1920x1200? That said, if it's working for your colleague, but not you, it further emphasizes that Lenovo is who you should contact because you haven't ruled out the unit is fully functional. – Allan Feb 22 '18 at 11:46
  • I wouldn't assume that the 20px difference is what makes the docking unit fail to drive the screen, but whatever. – Quaker Feb 22 '18 at 11:49
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Multiple monitors connected as your by DisplayPort (and/or HDMI converted from DisplayPort) served by a USB-C dock won't work on macOS. It will work on Windows, which is what Lenovo advertises.

For macOS you'll need a Thunderbolt dock instead to be able to do this.

A different solution is to plug one monitor into the dock, and the other monitor into the Mac. However you'll need to connect two cables to the computer this way, which is probably what you want to avoid when using a dock.

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