A common source for USB firmware and eMMC dumps for the MS638 series, available at KenotronTV.ru .
Format a USB drive to FAT32 . Copy only the extracted firmware file to the root directory of the drive. Flash: Power off the TV and insert the USB drive. Download MS638 PC822 3840x2160 Mitashi Ref35 part03 rar
Often hosts eMMC pinouts and software for this board at Remont-Main.ru . A common source for USB firmware and eMMC
Due to the technical nature of these files, they are usually hosted on specialized technician forums or cloud drives: Download MS638 PC822 3840x2160 Mitashi Ref35 part03 rar
Ensure you have all parts of the archive. Use a tool like WinRAR or 7-Zip to extract the main firmware file (usually named allupgrade_ms638_sos.bin or similar).