RAR archive of 740 KB for the Sony MBX-202 mainboard with ODM project code M790, marked as decrypted. That tag usually means a protected PDF schematic has been unlocked so it can be opened, searched and printed in a normal viewer. The drawings let a technician trace power rails from the adapter input through the charger and regulators, find components and check signal paths. Make sure the MBX-202 marking on the board matches, and compare the revision on the title block with your PCB.
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.