The 2SD1159 transistor is documented in this 77.0 KB PDF, catalogued with schematics but most likely the manufacturer datasheet given its plain part-number name. In the Japanese JIS scheme, 2SD identifies an NPN bipolar part intended for low-frequency operation. Check the pinout diagram and the maximum collector-emitter voltage, collector current and power dissipation listed there. Do this before fitting a replacement, and confirm the package and mounting style match the footprint on the board.
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.