Part documentation for the 2SB1287 in a 63.5 KB PDF; the 1-2 in the name probably marks pages one and two of the sheet. No device or board details are included. In JIS terms, a 2SB number identifies a PNP low-frequency bipolar transistor, often used in power and audio circuits. Technicians consult it for lead identification, voltage and current limits and dissipation. Check whether a separate file holds further pages, and confirm the package and pin order before fitting a replacement.
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.