Apple MacBook logic board schematic for project code M42C, labelled MLB (main logic board), in a 1.21 MB RAR archive. Apple uses internal codes such as M42C for board designs, and the matching 820 board number printed on the PCB identifies the exact one. The PDF lets technicians trace power rails from the charger through the SMC controlled sequencing, locate components by reference designator and find test points. Compare the board number on your logic board with the schematic before relying on it.
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 @generalschematics. 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.