DisplayPort port display won't work on mid-2020 Intel MacBook Pro

I just got my dock and tried to get it working with two Samsung monitors going through a dual-display KVM, which works great with another dock (the other dock only does 60W power though!).

Unfortunately, using the HDMI/DP dongle included, I cannot get the second display to work through the Plugable dock. My system just plain does not recognize it at all. I don’t know if the dongle is bad, or the DP port is bad, or something else? How do I diagnose the problem?

Hi Ian,

Thanks for posting! Sorry to hear about this display issue through your Plugable TBT3-UDC3 dock.

Firstly, you mentioned the use of a dual-display KVM. What if you temporarily remove the KVM from the configuration, and directly connect the TBT3-UDC3 dock directly to your MacBook Pro 2020?

Next, can you confirm you are using the original Thunderbolt 3 cable that came with your dock?

Thanks for giving us a chance to help!


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The dock is between the KVM and my MacBook, and using the original TB3 cable from your packaging. I rewired everything to only use the dock, and the DP port still doesn’t work. Everything else does. I’ve tested everything but the Ethernet port.

Thanks for clarifying.

Just be to clear here, is one out of the two Samsung monitors working (presumably through the HDMI port on the TBT3-UDC3 dock)?

Next, let’s perform a power-cycle of the unit in case the dock may be in an odd display state. To do so, please follow these steps:

  1. Disconnect all USB peripherals and displays connected to the dock
  2. Disconnect the docking station from the host machine, then disconnect the power adapter from power
  3. Leave unplugged for 1 minute for power to dissipate
  4. Connect the docking station initially into power only
  5. Connect the docking station to host machine, then connect USB peripherals and the two displays and test for functionality

If that still doesn’t help, I’d like to request some logs from your Mac to best investigate further. Could you please keep the dock connected to the MacBook Pro (with the non-working display still attached), then navigate to our PlugDebug tool and follow the instructions there?

Please just send that ZIP file the tool creates to us directly at support@plugable.com. You may include “Ticket #327627” so that we can match up the details to this post accordingly.

Thank you for your patience!


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I’ve done steps 1-5 several times. I can get either monitor to work by swapping the plugs, but I cannot get both to work at the same time. I’ll do the PlugDebug tool next.

Wow this software scanner is pretty invasive. I looked at the information it’s sending to you and it will contain sensitive information that I’m not comfortable sending via Email. I’m sure glad I did, too.

Why do you need a full list of every process running, every network, every audio device, every bluetooth device, every printer on my network, my cameras, every application I have installed (and where) and when I last used it, my firewall settings, every font I have installed, every log file on my system, everything stored in NVRAM, every preference setting in my system … seriously???

I’d rather hop on a Zoom call with someone from your support team to look at smaller, precise pieces of information you ACTUALLY need to debug this process. I cannot send this information to you.

Why do you need a full list of every process running, every network, every audio device, every bluetooth device, every printer on my network, my cameras, every application I have installed (and where) and when I last used it, my firewall settings, every font I have installed, every log file on my system, everything stored in NVRAM, every preference setting in my system … seriously???

To summarize it briefly, different aspects of the logs help us troubleshoot different issues. As one example, the list of applications installed allow us to check for potential display application conflicts. I would clarify that the data collected is not personal information such as application or network passwords, stored credit card information, addresses, etc, and the details of the tool can be found here under “Background”: https://plugable.com/support/plugdebug/

That being said, if you do not wish to send us the diagnostics, I certainly understand, and we’ll do our best to proceed without them.

I would like to start by confirming that the TBT3-UDC3 is operating at 40Gbps, which can be seen under your System Report > Thunderbolt tab. See screenshot below for an example:

Your mention that either monitor works by swapping connections to the DP and HDMI ports on the dock would suggest that the two ports should be working fine, so that is interesting to note.



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No, I cannot use the DP port at all. What I meant was that I can swap which monitor goes to the HDMI-only port and that works just fine (same when I was on the KVM as well, the DP port has never worked). Whichever monitor I plug into the DP port using the provided dongle does not display anything at all. Which settings can I show from the dump/log to show what it detects there?

Yes, definitely getting 40Gbps on the dock:


  Vendor Name:	Plugable
  Device Name:	TBT3-UDC3
  Vendor ID:	0x173
  Device ID:	0x2010
  Device Revision:	0x1
  UID:	0x01736F2D28920400
  Route String:	3
  Firmware Version:	58.1
  Port (Upstream):
     Status:	Device connected
     Link Status:	0x2
     Speed:	Up to 40 Gb/s x1
     Current Link Width:	0x2
     Link Controller Firmware Version:	1.42.0

Graphics/Display, just in case:

Intel Iris Plus Graphics:

  Chipset Model:	Intel Iris Plus Graphics
  Type:	GPU
  Bus:	Built-In
  VRAM (Dynamic, Max):	1536 MB
  Vendor:	Intel
  Device ID:	0x8a53
  Revision ID:	0x0007
  Metal:	Supported, feature set macOS GPUFamily2 v1
Color LCD:
  Display Type:	Built-In Retina LCD
  Resolution:	2560 x 1600 Retina
  Framebuffer Depth:	30-Bit Color (ARGB2101010)
  Main Display:	Yes
  Mirror:	Off
  Online:	Yes
  Automatically Adjust Brightness:	No
  Connection Type:	Internal
  Resolution:	2560 x 1440 (QHD/WQHD - Wide Quad High Definition)
  UI Looks like:	2560 x 1440 @ 144 Hz
  Framebuffer Depth:	30-Bit Color (ARGB2101010)
  Display Serial Number:	HNKN903281  
  Mirror:	Off
  Online:	Yes
  Rotation:	Supported
  Automatically Adjust Brightness:	No
  Connection Type:	DVI or HDMI
  Adapter Firmware Version:	5.04

I have two of the LC27G5xT monitors, identical models, side by side, in 2560x1440/144Hz configurations. Current dock works, current KVM works, but both are plugged in with HDMI cables since my KVM is HDMI based … so either the DP port on the Plugable dock isn’t working, or the dongle isn’t working. Unfortunately I don’t have any other full-sized DP cables to test, but I can maybe hit Best Buy for a cable or dongle later tonight.

Ah, I appreciate the clarification there. You’ve followed up one by one with the answers to questions I was going to ask!

While the TBT3-UDC3 dock officially supports up to 60Hz, 144Hz should theoretically be possible in terms of video bandwidth. Just to help rule out a weird bandwidth issue, what if you drop the refresh rate of the Samsung monitor connected via HDMI to 60Hz, then connect the other monitor to the DP input (using the including DP to HDMI adapter)? Does that still result in no signal?

In the meantime, could you reach out to us at support@plugable.com with the Amazon Order ID associated with your dock? Should we find either the DP port on the dock or the DP to HDMI adapter be faulty, we’d be glad to send you a replacement right away.



Hi again, sorry for the delay.

With both monitors switched to 60Hz, I get the same results. Only one monitor can be used at a time. Whichever monitor is plugged into the DP port does not work and is not detected by the MacBook. I’ll email my order ID to the support email address. Again, this was tested with no KVM in between, this was straight from the monitors to your dock to my MacBook using your provided TB3 cable.

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