Apple logic board 820-2179 is the only detail given for this 1.54 MB zip, with no Mac model, revision or archive contents stated. Packages of this kind usually contain schematic pages and sometimes a boardview. Schematics open in a PDF reader, while boardviews need a viewer such as OpenBoardView. Technicians rely on them to follow power sequencing, locate test pads and identify the component behind a shorted rail. Verify that the 820 number on the board matches, and note any revision in the documents before comparing measurements.
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.
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Compressed archive that every operating system opens without extra software.