For the 2SC4631 transistor, the index holds this 97.9 KB PDF, categorised as a schematic but evidently a component datasheet. JIS numbering uses 2SC for NPN bipolar devices. The name states nothing beyond the part number. A matching LS variant sheet is also listed in the set. Consult this one for maximum voltage and current, power dissipation, pinout and package dimensions, then confirm that the printed code on the board matches before ordering or fitting a replacement.
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 @cyberlanelectonik. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.