Named 121nq with no suffix, this 93.9 KB PDF is filed as a schematic yet states no device, board number or revision. The code resembles a rectifier series name, so it most likely documents a family of related parts rather than a board. Any PDF reader opens it. For diagnostics, the ratings tables and package drawing help when testing or replacing a suspect power diode. Read the exact grade from the part itself, because a series sheet lists several voltage variants.
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.