Part datasheet, most likely, for the 2SA1312 transistor, supplied as a 323 KB PDF and indexed under schematics. The 2SA code belongs to the JIS system and designates a PNP bipolar device. Technicians consult it to confirm emitter, base and collector positions, read maximum ratings and electrical characteristics, and evaluate cross-reference substitutes. No manufacturer, date or document revision is stated in the name, so verify that the package shown matches the component on the board.
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.