Apple logic board 820-2936, revision B, is the subject of this 1.75 MB zip archive; no model appears in the name. The package most likely holds a schematic and possibly a boardview for that revision. With these a technician can follow the power-on sequence, check standby and main rails, locate components and test points and trace a short to its source. Use a PDF reader for the diagram and OpenBoardView or FlexBV for layouts, and confirm the revision letter on the PCB since revisions can differ.
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.
How to open a .zip file
Compressed archive that every operating system opens without extra software.