Summary
The USBC-MSTH2 is a driverless USB-C to dual HDMI MST video adapter. If one or both displays are not working as expected, the most important items to check are the host computer's USB-C video capability, operating system display mode, graphics driver version, HDMI cables, and monitor compatibility.
The adapter does not require a Plugable driver. However, it relies on the host computer's built-in graphics hardware, USB-C DisplayPort Alternate Mode support, and Multi-Stream Transport (MST) support.
Applicable To
- Plugable USB-C Dual 4K HDMI MST Display Adapter (USBC-MSTH2)
- Windows 10, Windows 11 or newer, and ChromeOS 100 or newer
- USB-C, USB4, Thunderbolt 3, or Thunderbolt 4 host ports that support DisplayPort Alt Mode and MST
- Up to two HDMI displays connected through the adapter
Answer
Start by confirming that the computer, cable path, and display settings meet the requirements for the USBC-MSTH2.
The USBC-MSTH2 must be connected directly to a USB-C, USB4, or Thunderbolt port that supports DisplayPort Alt Mode. For two independent extended displays, the host system must also support MST. If the host system does not support DisplayPort Alt Mode, the adapter will not provide video output.
On Windows and ChromeOS, make sure the displays are set to extend rather than mirror. On macOS, dual extended displays are not supported with this adapter because macOS does not support MST for multiple independent displays through MST hubs. In most cases, macOS will show one extended display and one mirrored display instead of two separately extended displays.
Driver and System Update Checks
The USBC-MSTH2 does not require a separate driver from Plugable. It uses the host computer's native graphics output through USB-C DisplayPort Alt Mode.
Even though the adapter is driverless, display behavior can still depend on system software. For best results:
- Run Windows Update or ChromeOS updates
- Install the latest graphics driver from the computer manufacturer or GPU manufacturer
- For Windows systems, check Intel, AMD, or NVIDIA graphics driver updates as appropriate
- Install BIOS, firmware, or Thunderbolt firmware updates from the computer manufacturer if external display issues continue
- Restart the computer after installing updates
Graphics driver and firmware updates can help resolve missing displays, incorrect resolution options, flickering, blank screens, or displays that mirror when they should extend.
Connection Checks
Check the physical connection path before troubleshooting software settings.
- Connect the USBC-MSTH2 directly to the computer
- Avoid connecting through another dock, hub, extension cable, or USB-C adapter during testing
- Use the adapter's built-in USB-C cable and make sure it is fully inserted
- Connect each monitor directly to the adapter with an HDMI cable
- Use HDMI cables rated for HDMI 2.0 or higher when trying to use 4K 60Hz
- Confirm each monitor is set to the correct HDMI input
- Test each monitor and HDMI cable individually if one display works and the other does not
The USBC-MSTH2 draws power from the host computer's USB-C port. It does not use an external power adapter.
Display Mode Settings
On Windows:
- Open Settings.
- Go to System > Display.
- Select Detect if one display is missing.
- Under Multiple displays, choose Extend these displays.
- Select each display and confirm the resolution and refresh rate.
On ChromeOS:
- Open Settings.
- Go to Device > Displays.
- Disable mirroring if it is enabled.
- Arrange the displays as needed.
- Confirm the resolution and refresh rate for each display.
If the displays are mirrored on Windows or ChromeOS, the system display settings may need to be changed. If the displays are mirrored on macOS, that is expected behavior for this MST adapter.
Host System Requirements
The USBC-MSTH2 depends on the video capabilities of the host computer. The USB-C port must support DisplayPort Alt Mode, and the system must support MST for two independent extended displays.
Thunderbolt 3, Thunderbolt 4, and USB4 ports can be compatible when they carry DisplayPort Alt Mode and support MST. However, not every USB-C port supports video output. Some USB-C ports support data or charging only.
If the computer specifications do not clearly list DisplayPort Alt Mode, MST, or the DisplayPort version supported over USB-C, contact the computer manufacturer for confirmation.
Expected Resolution by Host Capability
The adapter does not create additional video bandwidth. It splits the video signal provided by the host computer. Because of this, the maximum resolution depends on the host system's DisplayPort capability and available bandwidth.
Display Stream Compression (DSC) is a display technology that allows higher resolutions and refresh rates to fit within the available DisplayPort bandwidth. For dual 4K 60Hz, DisplayPort 1.4 with DSC is recommended.
macOS, iPadOS, and Mobile Device Expectations
The USBC-MSTH2 is designed primarily for supported Windows and ChromeOS systems.
macOS and iPadOS do not support MST in the same way as Windows and ChromeOS. Because of this:
- macOS is not recommended for dual extended displays with the USBC-MSTH2
- A Mac may show one extended display and one mirrored display
- iPadOS supports only one external display
- Many phones and tablets do not support dual independent external displays through MST adapters
For Mac users who need multiple extended displays, a DisplayLink-based adapter or docking station may be a better fit, though those products require driver installation.
Common Symptoms and What They Usually Mean
Need Assistance?
If the USBC-MSTH2 is still not working as expected after checking the items above, contact Plugable Support at support@plugable.com. Please include the computer model, operating system version, graphics adapter, monitor models, HDMI cable type if known, and a description of what each display is doing.
