PDF of 119 KB for the 2SD1664, written in lowercase in the original name and filed as a schematic. The JIS code 2SD identifies an NPN bipolar transistor for low-frequency or power applications. Datasheets of this kind list maximum voltages, collector current, power dissipation and gain ranks, plus the package outline. Technicians use them to identify terminals, test the part out of circuit and choose an equivalent. Open it in any PDF viewer and verify the marking on the board matches.
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.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.