A compact 30.6 KB PDF tied to the 2SD1666 part number, catalogued among schematics. In Japanese JIS designations, 2SD stands for an NPN bipolar transistor meant for low-frequency or power stages. The small size suggests a short sheet, probably only key ratings and a pinout drawing. That is usually enough to confirm lead order and check voltage and current limits when substituting. Compare the device marking, commonly abbreviated D1666, with the document before trusting it for a repair.
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.