Datasheet-style PDF of 83.8 KB named for the 2SD1940, an NPN transistor under Japanese JIS numbering, in which 2SD stands for NPN low-frequency types. Although catalogued as a schematic, it is not tied to any specific device or board in the name. Use it when a power, driver or audio stage has a failed transistor: it shows the terminal order, breakdown voltages and current limits needed to choose a correct substitute. Check the printed marking, often shortened to D1940, and the case style before ordering parts.
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.