10. Flash EFI firmware
If your Mac is locked by the EFI password, you may see the flashing Mac folder with question mark. This password is different from the password that you use to set up the macOS account. The EFI password is stored in the EFI chip soldered on the logic board. It will lock the whole logic board. You can not use the option key function to guide the logic board to boot from an external HDD or simply replace the internal hard drive.
By contrast, the macOS account password is stored in the hard drive. You can get rid of the password by erasing the macOS completely or simply put another hard drive in the Mac. In other words, macOS account password protects the data in the hard drive while the EFI password prevents unauthorised access to the logic board.
There are a lot of reasons why the Mac is locked by EFI password and we are not going to address the reasons in this guide. We emphasize on how to remove the EFI lock.
There are two ways to fix this problem, replacing the whole logic board and clearing the password code stored in the EFI chip. We discuss the latter method here.
1. Remove the EFI chip from the logic board
2. Place the chip to the EPROM programmer
3. Read the EFI code and save as a file
4. Use a hex editor to open the file you just have saved.
5. Search for $ssv and replace the current row and next 12 rows with hex FF. This will clear the EFI lock code.
6. Write back the modified EFI code to the chip.
7. Solder the chip back to the logic board.
Congratulations! If you come up to this point, you just pass the intermediate level and enter into the advanced level of fixing Mac folder question mark issues.
The following “Mac folder question mark” case studies are hardware related and require chips replacement known as component-level repair. In order to perform the repair task, you need to have the micro-soldering skill, Apple mac logic board electronic diagram ( schematics) knowledge and some equipment
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