Archive for Apple board 820-2249, 1.60 MB in RAR format. The name holds nothing beyond the board number, so the revision and exact contents are unknown until it is unpacked; a package this size usually means schematic sheets. Apple uses the 820 prefix for its logic board part numbers, printed on the PCB near the edge or under the label. Confirm that number before working, then use the drawings to trace rails, read the power sequence and find the part pulling a line to ground.
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 @Mac_Shematic_Santale. 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.