Firmware package for a 49-inch RCA LED television, built on an MStar MSD338 platform with 4G noted in the name and the reference ref66. At 312 MB the RAR archive is large enough to hold a full software image, likely for an eMMC-based board or a USB update. Check that the main board and its markings match MSD338 and the stated reference before flashing. Keep a backup where possible, and use a stable power source during the update to avoid bricking the board.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @hashmielecom. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.
7-ZipWinRARThe Unarchiver (macOS)