Indexed as a schematic, the 217 KB PDF 2SD1412A most likely holds the datasheet for that transistor, where the A suffix marks a variant of the 2SD1412. Per the JIS scheme, 2SD parts are NPN bipolar transistors for low-frequency work. Consult it for package outline, lead functions, breakdown voltages and characteristic graphs when diagnosing or substituting. Compare the suffixed version's ratings with any proposed equivalent, and look for D1412A printed on the case.
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.