USB Lock (system lock) function is under "Debug/Player Setting".
There're two methods to unlock when it's locked.
1. Unlock by "Power Key Upgrade Procedure"
(1) Format the USB disk as FAT32.
(2) Extract upgrade file to the USB flash (FAT32) in the root directory. You will get "upgrade_510" folder. Insert USB flash into the USB2.0 port of the TV board next to the HDMI 1.
(3) Power on the display. Press the POWER key and hold it for 6 seconds until the power LED twinkles in red and blue.
(4) It will upgrade TV firmware firstly. When finished, it will reboot and upgrade MCU automatically. It will take 3 minutes to complete the upgrade procedure.
2. Unlock by USB flash
(1) Format the USB flash as FAT32.
(2) Unzip the attachment and copy to the root of USB flash.
(3) Insert the USB flash to Mainboard USB port
(4) System will unlock automatically