Reference PDF covering the 2SK1842, a part number in the JIS 2SK series used for N-channel field-effect transistors. At 30.3 KB it is a short document, likely a datasheet with absolute maximum ratings, electrical characteristics and package drawing. The name states nothing beyond the part number. Before ordering a replacement, read the pin layout from the sheet and compare it with the footprint on the PCB. Any alternative part needs equal or better voltage and current ratings and a compatible gate threshold.
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.
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The standard format for schematics, block diagrams, power-sequence charts and service manuals.