Apple board 820-3298 is referenced by this 2.63 MB zip archive, which names no model or revision. The larger size suggests it may contain both a schematic and a boardview. These are used to trace the power path from the charger input through the main rails, confirm component values and find a shorted line on the board. Schematic PDFs open in any reader and boardviews in OpenBoardView or FlexBV. Check the number and revision letter printed on the logic board before following the documents.
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 @notebookschematic. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.