Datasheet PDF of 248 KB for the 2SC3138, an NPN bipolar transistor going by its Japanese JIS 2SC prefix. Though indexed as a schematic, a lone part number like this normally means component documentation. The body marking is typically shortened to C3138. Package and manufacturer are not named, so check them inside. Use the pin diagram to orient probes for junction tests, compare voltage and dissipation ratings with the circuit, and confirm footprint and lead order before soldering in any substitute part.
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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