PDF datasheet for the 2SD879 transistor, roughly 106 KB, with no manufacturer indicated in the file name. Following the JIS numbering convention, the 2SD prefix denotes an NPN transistor intended for low-frequency service. The document is useful for reading pin assignment, package dimensions, absolute maximum ratings and typical characteristic curves while troubleshooting amplifier or regulator stages. Before substituting another type, compare voltage, current and dissipation limits and make sure the footprint and pinout line up with the 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 @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.