Mac BootROM manual update

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  • reformatt
    Badcaps Legend
    • Feb 2020
    • 1398
    • Australia
    #1

    Mac BootROM manual update

    So following on from this thread, I've been meaning to work out a way to update these boards manually without either having to pull the PROM or doing a reinstall of MAC OS. If I'm just fixing a board, I should be able to just update like you do on a PC laptop right? Well this is an Apple product......

    Firmware is well hidden in the installer. But once you've found it, you can just dump it on a memory stick or a spare SSD with Big Sur installed. Many thanks to StarterGo on GitHub for the pointers. I've done this for Macbook Air 820-3437 and 820-00165 boards, but other non T2 machines could be done similarly using the right firmware file.

    1. Download MAC OS installer via Terminal (firmware for 2013/14, and 2015/17 models are in this installer)

    softwareupdate --fetch-full-installer --full-installer-version 11.7.4

    Alternately, you can use Core Legacy Patcher GUI to download the installer.
    https://github.com/dortania/Opencore...tcher/releases

    2. From Applications folder, hold Control and select Install Mac OS Big Sur, Open Package Contents.

    3. Open Contents/SharedSupport/SharedSupport.dmg.

    4. Open SharedSupport from Desktop

    5. Open com_apple_MobileAsset_MacSoftware_Update

    6. Locate zip file in this folder and open it (will be long file name like cd4506......5C26.zip, should be around 11.5GB in size).

    7. Firmware located under AssetData/boot/EFI/EFIPayloads. Filename corresponds to each model

    MBA61.scap Macbook Air 2013/14 (820-3437)
    MBA71.fd Macbook Air 2015/17 (820-00165)

    8. Drag firmware file required to Desktop while holding Option key (copy)

    9. Check SIP status via Terminal
    csrutil status

    If enabled, you must reboot to Recovery Mode to disable, either CMD+R or external USB.

    10. Disable SIP. From Terminal, enter
    csrutil -disable

    11. Reboot back to MAC OS.

    12. From Terminal enter
    820-3437 boards:
    sudo /usr/sbin/bless -firmware ~/Desktop/MBA61.scap --verbose --recovery

    820-00165
    sudo /usr/sbin/bless -firmware ~/Desktop/MBA71.fd --verbose --recovery

    Enter password when prompted.

    13.Shut down the MAC i.e. power off (do not select reboot).

    14. Power on system, firmware update should complete and reboot.

    15. In MAC OS, confirm firmware has been updated.
    474.0.0.0 for 820-3437
    476.0.0.0 for 820-00165

    16. Reboot to recovery console, re-enable SIP via Terminal
    csrutil enable
    Tags: None
    • alassane.dontavius
      Banned
      • Jan 2023
      • 28
      • USA
      #2
      Re: Mac BootROM manual update

      btw u can update T2 bridgeOS same way, if you have T2 on very old version of bridgeOS you can update to 7.2 offline instead of the latest bridgeos 7.4

        Comment

        • dellxps15
          Badcaps Legend
          • Feb 2014
          • 1585
          • italy
          #3
          Re: Mac BootROM manual update

          tnx man, tried it today and worked like charm

            Comment

            • reformatt
              Badcaps Legend
              • Feb 2020
              • 1398
              • Australia
              #4
              Re: Mac BootROM manual update

              Addendum to this guide. Very old BIOS versions don't recognize APFS formatted drives, hence Big Sur created above will not boot. Technically, you could just run Big Sur/Monterey installers to update, but this is a PITA. So need to create a MAC OS SSD with HFS+ formatting. Newer versions of MAC OS don't support that, but High Sierra does. The problem here is that the installer script auto converts the SSD from HFS+ to APFS during installation, but this can be overridden.

              Create a HFS+ (MAC OS Journaled) formatted High Sierra installation SSD

              1. Boot to Recovery mode via a High Sierra USB installer, with a spare SSD fitted to install High Sierra on.

              2. In Disk Utility, format the SSD as Mac OS Extended (Journaled), call it Macintosh HD.

              3. Open Terminal and disable SIP, otherwise following command will not work:

              csrutil disable

              Reboot the machine, and boot from the USB installer again.

              4. Open Terminal and run

              /Volumes/"Image Volume/Install macOS High Sierra.app"/Contents/Resources/startosinstall --volume /Volumes/Macintosh\ HD --converttoapfs NO --agreetolicense

              Syntax here is very important. If you get an error, check things like Volume or Volumes and spacing.

              5. Once the setup is complete, create a user account and password. Don't bother with any updates (don't think they work anymore from the outdated App store in this version anyway).

              6. Insert the Big Sur USB installer, and extract the firmware files as listed previously.

              7. Update firmware using the Bless commands as before:

              820-3437 boards:
              sudo /usr/sbin/bless -firmware ~/Desktop/MBA61.scap --verbose --recovery

              820-00165
              sudo /usr/sbin/bless -firmware ~/Desktop/MBA71.fd --verbose --recovery

              As of 15/11/2023, current firmware versions are:
              476.0.0.0 for 820-3437
              481.0.0.0 for 820-00165

              8. Re-enable SIP from recovery mode

              csrutil enable

                Comment

                • David Sage
                  New Member
                  • May 2025
                  • 1
                  • India
                  #5
                  Not working for MBP114

                    Comment

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