Named simply 80SQ, this 125 KB PDF is indexed as a schematic, but the code looks like a series designation for a rectifier diode family rather than a circuit diagram, and no device or board is stated. Expect a component datasheet covering several grades of the series. A technician would use it to confirm ratings, polarity marking and package before testing or replacing a diode. Because the name lacks a grade number, match the full marking on the component against the tables before relying on any value.
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.