Zip archive for the Apple logic board 820-3787, revision A, 3.95 MB. The name gives no Mac model or file list, so check whether it holds a schematic, a boardview or both. Apple prints 820 numbers and revision letters on the logic board, and those must match the documents before you trust component locations. Technicians use such material to trace power rails, find test points, follow the power-on sequence and isolate a shorted part. Boardview data opens in OpenBoardView or FlexBV, and schematics in a PDF reader.
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.