The 2SC5122 is named in this 171 KB PDF, which the index lists under schematics even though the title is only a component number, suggesting a datasheet. JIS designations with the 2SC prefix belong to NPN bipolar transistors, normally marked C5122 on the package. The document is useful for identifying the pinout and case style, reading limit values such as maximum collector voltage and current, and comparing gain and frequency figures with candidate replacements when the original part cannot be sourced.
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.