Here the 2SC5231 is covered by a 133 KB PDF that the catalogue files under schematics, although it most likely is a transistor datasheet. Under JIS designations, 2SC means an NPN bipolar transistor. The name carries only the part number. Open the sheet in a standard PDF reader for collector and base limits, gain figures, package type and pin identification. Check the device code on the board first, because similar numbers in this series belong to different transistors.
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.