Datasheet for the 1N5231C in a 62.9 KB PDF, catalogued under schematics. The 1N52xx numbers belong to a well known zener diode series, and the C suffix usually indicates a tighter voltage tolerance grade than the A or B versions. Look up the zener voltage, test current and power dissipation here when checking a reference or clamp diode. Any PDF viewer opens it. When substituting, keep the same voltage and tolerance class, and confirm the package and cathode marking match the original.
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.