Apple board 820-2143 documentation in a 1.33 MB RAR archive, with no schematic code, revision or board role stated in the name. Its size is in line with full logic board schematics elsewhere in the series, but confirm the contents once extracted. Apple numbers PCBs as 820-xxxx, and the code printed on the board must match before you trust any net or part reference. Such drawings are used to trace power rails, follow signal paths and pin down the component responsible for a short or a no-power fault.
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.