Apple logic board archive for board 820-2936, a RAR of about 2.70 MB; the lb prefix stands for logic board. Apple numbers its main boards in the 820-xxxx format, and that number is printed on the PCB itself, so read it there instead of relying on the model year. The name does not say whether the package holds a schematic, a boardview or both. Use the material to trace PP rails, measure resistance to ground on suspect lines and locate parts. Make sure the board revision on your unit matches before trusting values.
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 @alischematics. 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.