Apple schematic in PDF form for logic board 820-2031, with the associated 051-7124 drawing number and the L000 tag, about 1.61 MB. The 820- prefix is Apple's own board numbering and 051- marks the schematic document number. A PDF reader is enough to open it and search net names. Technicians use it to trace power rails, follow signal paths, find component references and diagnose shorts. Confirm the 820 number silkscreened on the logic board before relying on the pages.
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 @cynetitsolution. 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.