Apple firmware archive for logic board 820-2542, revision A as given in the name, roughly 4.33 MB in RAR form. Apple uses the 820-xxxx series to identify logic boards, so the number printed on the PCB is the reliable way to confirm a match instead of the model name. Such dumps are used to rewrite the EFI or boot ROM SPI chip when a Mac shows no chime or a firmware lock. Extract and check the image size against the installed flash, save a read of the existing chip and verify the board number before programming.
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 @biosarchive. 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.
Back up your own chip before writing any dump, and match the full board number and revision. Flashing guide →