Reference datasheet in PDF format, about 133 KB, describing the 2SD826 transistor; the source manufacturer is not given in the name. As a JIS-coded 2SD part it is an NPN transistor designed for low-frequency operation. Use the document to identify the base, collector and emitter leads, read absolute maximum ratings and characteristic curves, and evaluate possible equivalents when the original is unavailable. Check the device marking and case style on the PCB first, since substitutes must match 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.