PDF schematic for Apple logic board 820-1550, packed in a 1.34 MB archive. Apple identifies its boards with the 820-xxxx pattern; the name gives no revision letter or Mac model, so check the silkscreen on your board before trusting values. A circuit diagram like this lets a technician follow the power-on sequence, check rails and signal names, and identify the parts around a fault such as a shorted line. Open the PDF in a standard reader and search by net or component reference.
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 @LaptopsBoardview. 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.