A PDF document for the 2SA1604, an 84 KB file listed in the index as a schematic but named after a single discrete part rather than a board. Under the Japanese JIS numbering system, the 2SA prefix marks a PNP bipolar transistor intended for high-frequency use. The file most likely holds the datasheet with ratings, pinout and package outline. Technicians use it to confirm the collector, base and emitter pins and the voltage and current limits before fitting a replacement. Check the part marking against the board 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.