A 1.11 MB RAR archive covering the Sony MBX-269 and MBX-268 mainboards, with HK5 and HK6 also listed in the name, which look like the related ODM project codes for these two boards. Two board numbers sharing one package suggests closely related designs that differ by variant, for example graphics or size. Inside you can expect schematic drawings for tracing power rails, signals and component locations. Check which of the two MBX numbers is printed on your PCB and match the corresponding sheet set before measuring.
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.