The 2SD2571 transistor is documented in this 101 KB PDF, indexed as a schematic though most likely a datasheet. Under the Japanese JIS standard, the 2SD prefix identifies an NPN bipolar transistor for low-frequency service. The name gives no manufacturer, package or revision. Technicians reach for this kind of sheet to check pinout and outline dimensions, compare electrical ratings against the circuit conditions, and evaluate substitutes when the original part is obsolete or hard to find.
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.