The user obtained the correct file ( 55XT_MSD3683_v2.3.bin ) from an official service partner. They performed a “forced bootloader update” by shorting pins 5 and 6 on the EMMC chip (not recommended for general users). The USB update succeeded on the second attempt.

The firmware was intended for a model with a Realtek RTD2851 chipset, but the user’s unit had an MStar MSD3683 chipset. The bootloader loaded successfully (logo appears), but the kernel failed to initialize the video decoder (bootloop).