Firmware image for Apple A1708 logic board 820-00840, revision A, described as tested and working, with an empty serial number field. Because the serial is blank, the dump is a clean template suited to a board whose EFI chip is corrupted; system serial and identifiers should be written back from the original. Read and keep the existing chip contents with an SPI programmer before flashing. Make sure the image size matches the flash device, and confirm the 820 board number printed on the PCB.
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 @hrtechno. 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 →