RAR archive labelled SN3 and SHINAI-3, codes that appear to be a project or model designation but give no brand, board number or revision with certainty. At 1.10 MB the size fits a compressed schematic or documentation set. Extract it with WinRAR or 7-Zip and read the title block to identify the manufacturer and board revision. Match those details against the silkscreen on the PCB before using it to trace rails, locate components or check signals, since uncertain files can mislead a diagnosis.
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 @generalschematics. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.