RAR archive for the X51C with the extra token T12C, about 1.50 MB. The name does not explain T12C. It may be a board or platform code, but treat it only as a marking to compare against your hardware. Extract the archive with WinRAR or 7-Zip to see whether it holds a schematic, a boardview or firmware. Use it to trace power rails and locate parts, or to reflash the BIOS chip. Check that the board markings match, and back up the existing flash before writing.
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 @IT_SERVICE_WORLD. 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)