The 2SD1229 is documented in this 126 KB PDF, which the index lists as a schematic. Its JIS number places it in the 2SD series of NPN bipolar transistors for low-frequency service. A datasheet of this kind usually lists maximum ratings, electrical characteristics, gain classification letters and the package outline. When servicing a board, compare the marking and lead layout with the drawing, test the junctions with a diode meter and ensure any replacement has equal or greater voltage and current limits.
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.