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I connect my MacBook Pro with Thunderbolt 3 to a Lenovo C-Dock, which connects 2 external monitors through 2 DisplayPort cables. The problem I have is that the 2 external monitors mirror each other.

MacBook Pro (15-inch, 2018)
macOS Mojave
Version 10.14.3 (18D109)

Lenovo USB-C Dock Type: 40A9

I looked at the display settings, and there is no options to change it. I also tried to connect one of the monitor through VGA port, the 2 monitors still duplicate.

How can I make the 2 external monitors display distinct content and not mirror each other?

8 Answers 8

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The MacBook only supports dual displays including the built in display. In other words, it will only support one external monitor. Per the tech specs:

Dual display and video mirroring: simultaneously supports full native resolution on the built-in display and up to 4096-by-2304 resolution at 60Hz on an external display, both at millions of colors

The Lenovo C-Dock doesn't enable your MacBook to supply more display bandwidth than Apple provides. So, the mirroring you are seeing is expected behavior.

From the comments...

...I should specify that my MacBook is actually MacBook Pro (15-inch, 2018). Would that make any difference?

Yes and no.

Yes in that the MacBook Pro (as opposed to the MacBook) can support more than 1 external monitor. However, as you've already discovered, if you connect them separately, it works. Unfortunately, you can't daisy chain monitors from a single port; you must use separate ones. Use of the dock still doesn't increase the available video bandwidth of the Thunderbolt/DisplayPort port even if the machine itself has the capability.

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  • Sorry, maybe I should specify that my MacBook is actually MacBook Pro (15-inch, 2018). Would that make any difference? It has 4 USB Type-C ports, one of them has to be for the charger. When I connect 2 monitors through the C port separately, they extended. So that way I have 3 different displays including the built in.
    – hxin
    Mar 22, 2019 at 15:36
  • Then the purpose to use the dock is meaningless in regards of extend displays. It may still be useful to have more USB ports, but that's about it. Does "more than 1 external monitor" mean I can connect 3 external monitors directly to the type c ports? (another one for charger)
    – hxin
    Mar 22, 2019 at 18:58
  • 3
    NOTE, the macbook pro 2017/18 DOES support 3 non-mirrored monitors - two external and the internal.. I have two external 2560x1600 displays connected via a single thunderbolt mini doc which has 2x DP out. However, if I use the thinkpad thunderbolt doc, it willy only mirror the two displays. This sucks. Jan 16, 2020 at 9:34
  • I have a MBP 13" 2019 and I can use the dock with mouse keyboard and one external display, for the second ext. display I was forced to use a separate cable (HDMI over usb-c mobile hub)
    – thst
    Jan 24, 2020 at 15:44
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    This is not a display bandwidth issue at all. The method that the Lenovo docks uses a technique not supported by MacOS, namely, DisplayPort MST. To prove that this is the case, load Windows 10 on to the Mac and the multiple extended monitors will work just fine. Apr 17, 2021 at 15:45
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The ThinkPad Docks use the DisplayPort Multi Stream Transport (MST) Hub standard on the two exposed DisplayPort ports. This technique allows multiple external monitors to act as extended screen area as long as the hardware and driver support MST Hub. Without MST Hub support, multiple external monitors on the dock can only act as mirrors of each other. Unfortunately, macOS does not support DisplayPort MST Hub. Only Thunderbolt chained monitors are supported. Presumably, Apple regards MST Hub as a legacy, dead-end technology.

This is not a bandwidth issue at all. If you run Windows 10 on the exact same Mac hardware, multiple monitors within the DisplayPort bandwidth work flawlessly as an extended desktop.

You can read more about DisplayPort MST technology at https://www.tripplite.com/products/multi-stream-transport-mst-hub-technology and https://www.caldigit.com/can-ts3-and-ts3-plus-support-displayport-multi-stream-transport-mst-feature/

Currently (April 2021), each Mac Thunderbolt 3 port supports only one display per Thunderbolt 3 port, and it needs to be the last one in the Thunderbolt 3 chain. I don't know for sure, but I suspect this refers to monitors using the DisplayPort Alternate Mode on the Thunderbolt 3 chain.

You can daisy chain multiple native Thunderbolt monitors on a single port. Once an adapter is introduced, the game is over.

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  • 1
    Your answer implies the only way to use more than one external display with a Mac is to daisy chain them over thunderbolt 3, but there are many people online who have gotten this to work with a thunderbolt 3 hub. Maybe you could elaborate on that alternative for the OP and future readers.
    – MegaMatt
    Jan 12, 2022 at 3:56
  • I think the “Thunderbolt hub” solution is consistent with “One DisplayPort endpoint per Thunderbolt port.” Jan 13, 2022 at 5:25
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Old topic, but figured I should share a new update:

The Lenovo Thinkpad dock will support 2 separate displays. I found that if I plug one into the back of the dock (displayport to displayport) and the other into the front of the dock (displayport to USB-C) it'll run them both as separate displays along with my MB Pro 16 display.

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  • I suppose this works because it does chaining for the display connected to the USB-C / TB port on the front. I get flicker on the display connected to teh HDMI port on the back, though. Feb 7, 2022 at 8:23
  • When you say "the new one," can you specify a model number? Feb 1, 2023 at 5:53
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I currently run 4 displays off a single USB-C port to a thunderbolt dock. I have 2 of the lenovo docks daisy chained and I only plug 1 USB-C cable into my laptop. If you are having an issue with it duplicating your display check your drivers and the setting on the dock.

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  • With macOS or Windows? This should not be possible on macOS. Feb 1, 2023 at 5:58
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This was working for me (15" MacBook Pro, 2018) with 2 Dell monitors connected using a ThinkPad Hybrid USB-C with USB-A Dock, with a single USB-C cable providing my laptop with power and driving the two external monitors as separate displays (not mirrored). Unfortunately that dock went back to work, and I bought a ThinkPad USB-C Dock Gen2, which looked similar. Using this dock, the external displays are mirrored. I have the DisplayPort software installed and I have tried everything I could think of. So I'm going to try and negotiate a return / replacement.

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  • This should not be possible with macOS. Unless the MacBook was running windows, you can only do two monitors with expanded desktop on daisy-chained Thunderbolt monitors or with two independent USB-C connections, one servicing each monitor. Feb 1, 2023 at 5:56
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i am using Macbook Pro m2 pro 14" with lenovo USB c gen 2 dock (LDC-G2), 03X7609 Type 40AS. if you refer to this - https://www.lenovo.com/content/dam/lenovo/pcsd/north-america/en/lenovo-partner-network/presentations/na-presentation-lenovo-docking-solutions.pdf

go to page 18, you'll see the USB C dock gen2 does not rely on displaylink tech. Which means it cannot be supported to display the second extended screen (3rd screen) without using a USB-C to HDMI (hopefully with displaylink) enabled.

i checked there's no new firmware update, and i went to view system settings on mac, indeed i couldn't find any traces of displaylink. I also installed displaylink manager 1.8.0 and 1.8.1 and it stated that it couldn't find any displaylink related device (no displaylink enabled display).

only if you're using the thinkpad hybrid USB-C and USB-A dock that you'll get the displaylink support, and it a hit-and-miss based on this post - https://forums.lenovo.com/t5/ThinkStation-Workstations/Thinkpad-Hybrid-USB-C-with-USB-A-Dock-compatibility-with-Macbooks/m-p/5134764

apparently, apple decided that multi-stream transport will be deprecated soon and has decided to cut it off early. https://forums.lenovo.com/t5/Displays-Options-and-Accessories/Lenovo-USB-C-dock-treats-2-monitors-as-one-with-Macbook-Pro/m-p/4365133

hopefully this saves all of you folks time since i've spent about 3-4 hours trying to figure this issue out.

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I solved this puzzle by connecting one of the monitors straight to the Macbook using a USB-C/HDMI cable. All the other stuff is connected to the docking still. One of my monitors has 3 ports, so, I pretty much have 2 cables connected to the same monitor. One running to the docking and the other to the Macbook. When I connect the docking station to my Dell/Windows laptop, it recognises both of the monitors from the docking, while the MacBook, ignores one of the connections and recognises the HDMI connected to the USB-C.

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A Work around I discovered is as follows in 2023/2024.

Tested with a MacBook Pro with a M1 Max(personal) and a MacBook Pro with an M2 Pro (work Provided)

Get the OWC Dual Display port adapter. It's Thunderbolt to Dual DisplayPort. (https://www.owc.com/solutions/thunderbolt-dual-displayport-adapter). make sure you have real thunderbolt cable, this was the hardest part, I went through several 'cables' from Amazon that were not really thunderbolt 4. I ended up buying an OWC branded one.

After that, both monitors work. There must be some chip extensions in there. I can use the two displays, and the onboard LCD just fine this way. It's not using the onboard DVI ports of the dock, and its a dongle, but it makes it all work.

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