RAR archive of 2.32 MB for Apple board 820-2849, named only by its board number with no revision, model or content notes. Apple's 820-xxxx numbers identify individual logic board designs, so confirm the number printed on your PCB. The archive may contain a schematic, a boardview or both; PDFs open in any reader and boardview files in OpenBoardView or FlexBV. Use them to follow rails from the DC input, find components by designator and trace where a short or missing voltage begins.
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.