The 2SC3125 transistor is covered by this 299 KB PDF, catalogued with schematics. Under JIS conventions 2SC denotes an NPN bipolar part, commonly printed C3125 on its package. The larger size suggests detailed characteristic curves or several pages of data, but the name gives only the part number. Open it in any PDF reader to check the pin order, absolute maximum ratings and outline dimensions, which help when testing the part in circuit and selecting a replacement that matches both electrically and mechanically.
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.
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The standard format for schematics, block diagrams, power-sequence charts and service manuals.