Component reference for the 2SD1993, a 45.5 KB PDF listed among schematics. Following Japanese JIS part numbering, 2SD identifies an NPN bipolar transistor of the low-frequency class. The name gives no manufacturer or package, and the E suffix is unexplained. A sheet like this lets a repairer read the pin assignment and maximum ratings, then test the device with a meter's diode or hFE function. It also helps when judging whether a different transistor can stand in for a failed one.
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.