Component datasheet for the 2SB1644, a small 48 KB PDF catalogued under schematics. JIS numbering places any 2SB part among PNP bipolar transistors for low-frequency use, and nothing else about the package or manufacturer appears in the name. A technician would consult it when a board fault leads to this transistor: the electrical tables give collector-emitter voltage, current and dissipation limits, while the outline drawing shows which leg is base, collector and emitter. Compare the marking code with the part on the PCB 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.