Document for the 2SK2400, 403 KB in PDF format and listed as a schematic, although the name points to a single-component datasheet. The JIS prefix 2SK identifies N-channel field-effect transistors. Beyond the part number the name says nothing about package or maker. Open it with any PDF reader to look up pin assignment, absolute maximum ratings and characteristic graphs, then compare these with the replacement you intend to fit, and confirm the case marking on the board matches first.
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.