Sony laptop documentation archive for model code MSS1 with board MBX-155, labelled revision 0.30Sec, which suggests an early or secondary revision of the drawings. At 1.29 MB the RAR most likely holds a schematic. The name marks it as a duplicate copy, so compare it with other versions. Schematics of this kind are used to trace power rails, check signal paths and locate components and test points during board-level repair. Match the MBX-155 marking and revision on your motherboard to the document before measuring or replacing parts.
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.