Reference sheet for the 2SD2550 transistor, a PDF of roughly 239 KB catalogued as a schematic. The 2SD prefix follows the JIS convention for NPN bipolar transistors aimed at low-frequency work. A repair tech would read it for the base, collector and emitter pin order, the absolute maximum ratings and the case style. Before ordering a replacement, confirm that the part marking on the PCB really matches this number, since similar codes can hide different packages.
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.