PDF documentation for the 2SK1731 discrete semiconductor, roughly 90 KB in size. Japanese 2SK numbering identifies it as an N-channel FET; the name says nothing about the manufacturer or package, so those details have to be taken from the pages themselves. A repair technician would consult it to identify pins while probing in circuit, to check whether a measured gate threshold or diode drop is plausible, and to choose a replacement with equal or better voltage, current and power dissipation figures.
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.