Part number 2SC4124 names this 98.7 KB PDF, which is labelled a schematic but, given the JIS-style designation for an NPN bipolar transistor, should be that part's datasheet. On the board the component normally reads C4124. Repair use centres on confirming collector, base and emitter positions, checking absolute maximum ratings and comparing gain and switching data when sourcing a replacement. The name gives no manufacturer, version or gain grade, so match the original part's suffix and case style before substituting.
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.