Datasheet in PDF form covering the 2N3773, catalogued as a schematic though the name points to a single-part reference for a 2N-numbered transistor. The trailing RE in the name is not defined and could indicate a revised edition; size is 205 KB. A sheet like this gives the absolute maximum ratings, characteristic curves and case drawing needed when checking a failed output stage or picking an equivalent. Open it in any PDF viewer and compare the case style and lead layout with the device on the board.
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.