Monitor Turns to a Black Screen When USB-C Prioritization Changes from High Data Speed to High Resolution

Affected Platforms:

• Dell Wyse 5070
• Dell Wyse 5470

Affected Products:

All monitors that support USB-C Prioritization:

• U4320Q
• U2520D
• U2421HF
• U2721DE
• U2421E
• U2422H
• U2422HE
• U2722D
• U2722DE
• P3222QE
• C2722DE

Affected Operating Systems:

• Dell ThinOS

Sample: USB-C Prioritization image - from U2520D monitor user guide

Figure 1 (English Only): USB-C Prioritization setting

How to Reproduce steps and behavior:

1. Connect a monitor which has a USB-C prioritization feature to a DELL Wyse 5070 thin client USB type C port using a Type-C to Type-C cable.
2. Power on the thin client and wait for the ThinOS desktop to display on the monitor properly.
3. Press the monitor On Screen Display (OSD) menu and select USB-C prioritization.
4. Change the setting from High Data Speed to High Resolution.
5. The monitor screen turns black, and the OSD shows that there has been no USB-C signal input detected. This is the reason why the video cannot be displayed.

ThinOS firmware does not support USB-C prioritization (this is due to the USB Type-C Connector System Software Interface (UCSI) specification). Hence, when the USB-C prioritization setting changes, the ports link training cannot properly establish to present the video on the monitor screen.

Work around

Force the thin client to restart.

Log term solution:

ThinOS 2311 (9.4.4106) or later resolves this issue.