Specification sheet, 85.3 KB in PDF form, for the 2SD1958 NPN transistor, indexed in the schematic section. Under the Japanese JIS system, 2SD designates an NPN bipolar part for low-frequency applications. The name says nothing about manufacturer, package or revision. The pages should cover electrical characteristics and mechanical outline. Read the pin diagram carefully, since lead order varies between packages, and match the marking on the part before installing a replacement.
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.