HDMI 3 and 4 not detecting monitors on plugable ud-3900c4 docking station

I am having issues getting two out of the 4 monitors I have to detect the plugable docking station.

I have a Predator Helio 300 gaming laptop and three Samsung monitors and one sharp monitor hooked to the docking station. HDMI 1 and 2 are detecting the monitors but HDMI 3 and 4 are not and i cant seem to get them to detect.

I have tried uninstalling and reinstalling the software multiple times without any luck.

Any help in resolving this is much appreciated.

Hi Andy,

Thanks for reaching out to Plugable support! I’d be happy to help with that.

Looking at the support information for this particular computer, it looks like the USB-C port does not support the required Alt Mode or MST that is necessary for HDMI ports 3 and 4 to function for this doc. It looks like this laptop also does not support laptop charging through the USB-C port.

In spite of this incompatibility with the laptop, you should be able to achieve connection to HDMI ports one and two, along with all other functionality except the additional 2 display connections and laptop charging.

Here are a few lengths that explain compatibility requirements for this docking station more more thoroughly.

How do I know if my computer supports Multi-Stream Transport (MST)?

What is the difference between the DisplayLink vs Alt Mode MST ports?

Thank you for giving us the chance to help.

Richard A
Plugable Technologies

I have the same problem with either a Dell or Microsoft Surface laptop - both are connect to the ud-3900c4 via a USB switch to allow for either to use the monitors (sort of a poor man’s KVM). I’ve also tried both laptops connected directly to the dock. I’d like to connect three Sceptre monitors and a Samsung HDMI TV as the output monitors. As @whitlow is experiencing, HDMI outputs 1 & 2 work but 3 & 4 do not. Is this the same issue Alt Mode/MST with the USB-C port ??? If so, two follow up questions … (1) What specific configurations are supported by this product ??? And (2) do you have other docking stations that support a wider variety of configurations ???

Thanks in advance for your reply.

Hi Andy,

Thanks for the update.

This definitely sounds like you are dealing with an issue with supporting Alt Mode or MST.

One thing to note about a KVM is it merely takes connections from an existing device and allows those connections to be switched to a different device. Docking stations like the UD-3900C4 utilize a single USB-C connection with the added support of Alt Mode and Power Delivery in order to break out all of those connections for the displays, multiple USB hubs, audio input, Ethernet and other connections that you have available on the dock.

I’m not aware of a KVM that will support a USB-C connection Alt mode or Power Delivery. There are full USB-C pass through switches that do exist, but they are very expensive and typically only found for industrial services.

Depending on which version of your Microsoft surface laptop you have, that may be able to support the full range of this stocking station. For example, we have tested and know that this docking station is fully supported by the Microsoft Surface laptop 3, 4, and 5.

I hope this information is helpful. And please let me know if you have any additional questions.

Richard A
Plugable Technologies