Reference PDF for the 2SD1220, 189 KB, listed among schematics though the number is a discrete transistor designation. The 2SD series under JIS covers NPN transistors for low-frequency circuits. Such documents normally give breakdown voltages, maximum collector current, dissipation, gain ranks and package information. A technician reads them to diagnose a shorted or open device, identify the terminals and choose a cross-reference part, confirming the pinout before soldering to avoid reversing collector and emitter.
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.