Apple logic board schematic for 820-3332 revision A, provided as a 2.39 MB PDF. Match the 820 number silkscreened on your board along with its revision before trusting component values. Use the pages to follow the boot and power sequence, read net names for rails and enables, check which components sit on a shorted line and identify unmarked parts by reference designator. Reading it next to a boardview of the same board makes locating those parts on the PCB much quicker.
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 @one5technology. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.