Reference sheet for the 2SC3990 transistor, stored as a 104 KB PDF and catalogued under schematics. The name gives no maker or application, only the JIS part number, where 2SC stands for an NPN bipolar transistor. Repair work typically relies on such a datasheet for the pinout, package outline and absolute maximum ratings, which matter when diagnosing a shorted junction or matching a replacement. Boards usually show the shortened marking C3990, so compare it and the case style before swapping parts.
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.