RAR package of 1.43 MB for the Apple logic board identified as 820-2507. The name holds only that number, leaving the Mac model, board revision and included file types unstated. Apple assigns 820-series part numbers to its logic boards and prints them on the PCB, so read that marking before using these drawings. Typical use is diagnosing no-power or no-boot faults: tracing the power-up sequence, checking rail voltages against the schematic and locating suspect components or test points on the board layout.
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 @Mac_Shematic_Santale. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.