At just 33.5 KB, this PDF for the 2SD1623 is a short document listed as a schematic, though the part-number name suggests a compact datasheet. The 2SD prefix, under Japan's JIS convention, denotes an NPN transistor for low-frequency use. Expect basic electrical characteristics, ratings and possibly a package outline, enough to confirm pinout and judge a replacement. Before swapping a part, compare package type and pin order with the original, since D1623 printed on the body is the usual shortened marking.
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.