RAR archive for a Sony VAIO motherboard numbered MBX-143, with the MS03 token in the name, which on Sony boards usually marks the ODM project or schematic code. At 1.57 MB it most likely holds schematic pages in PDF form, though the contents are not listed. Sony prints its own MBX numbers on the PCB while the actual design often comes from an ODM such as Foxconn or Quanta. Confirm that the MBX label on the board matches before tracing power rails, checking a short or locating test points with these sheets.
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 @generalschematics. 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.