HDMI-1 Alt mode not working on my UD-3900PDZ

My USB-C Alt Mode (HDMI 1) has not worked since day 1. I chalked it up to not having the right cable, but I have gone through various HDMI to USB C cables and I still have not managed to get it to work.

macOS Monterey
MacBook Pro (13-inch, M1, 2020)
Chip Apple M1

Displaylink 1.6.0 Build (59.128)

If this is a cable problem, could I perhaps get a suggestion as to which cables are compatible to power this port?

Hi Roy,

Thanks for contacting us! I am sorry this is not working as expected.

The UD-3900PDZ’s HDMI 1 “Alt Mode” output requires connecting the docking station directly to a USB-C port on the host computer with the USB-C cable included with the docking station. USB-C cables from other devices or products ( like the Apple USB-C charging cable ), or sold online as “charging” cables may not support USB-C DisplayPort Alternate Mode video data and will be incompatible with this docking station.

Additionally the M1 MacBook natively only supports one USB-C connected display, if there are any other USB-C or Thunderbolt connected displays connected directly to the MacBook they will take priority over the docking station’s HDMI 1 “Alt Mode” output port. The HDMI 2 and HDMI 3 output ports are controlled by the DisplayLink Manager App and are not counted against the computer’s single-display capability.

I recommend starting by ensuring the docking station is connected directly to the computer using the original USB-C cable provided with the docking station, no adapters, extensions or other devices between the computer and docking station. Also please unplug any other USB-C devices or displays from the computer to ensure the docking station receives display priority.

If this doesn’t help, our next step is to get some additional information from your system to check and see if the computer is detecting the docking station as a USB 3.0 device, or USB 2.0 device, if detected as USB 2.0 then it likely points to an incompatible USB-C charging cable.

If you would, please keep the dock connected to the computer with monitor(s) connected tot he docking station (even though one may not be working) and attach the output of our diagnostic utility PlugDebug ( http://plugable.com/support/plugdebug ) to an email to ‘support@plugable.com’ with the subject line ‘Ticket #370855 - Attention Pat’ as this will allow us to examine some log files from your system to help determine the next steps.


Plugable Technology

Follow up for future readers:

HDMI 1 ‘Alt Mode’ of the Unit was not at a 100%.

  1. Did the Plugdebug
  2. Sent pictures with various connections
  3. Sent video as verification

Plugable sent a replacement as part of their warranty coverage. Issue closed.

Thank you for providing a summary!

As previously stated this issue was resolved with a replacement and I am marking this thread as closed.

If you have any additional questions, or issues arise please feel free to start a new thread or contact our support team via email at ‘support@plugable.com’.

Have a great day!

Plugable Technologies