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I want to bring back my beloved Macbook Air 2012 (MBA5,2) to its 'original firmware'. I have identified the file as MBA51_00EF_B01.scap, which I extracted using unpkg over the downloadable offered by Apple here: MacBook Air EFI Firmware Update 2.5.

That version allows one to install OSX 10.7.4, which is the (oldest) OS that shipped with this machine. That will allow me to reactive an old M-Audio sound interface that only works with Lion OSX. But also to experience and use this hardware performing the lightest, for I mainly use it as a working station with vintage software.

Presently I have Mountain Lion (10.8.4) installed, but once I had El Capitan which upgraded me to BootROM MBA51.00EF.B04 and SMC 2.5f9. I managed to downgrade the SMC firmware to version 2.5f7, which is compatible with 10.7.4–I used rEFIt and SmcFlasher.efi for it. But Bootrom remains MBA51.00EF.B04.

I followed this guide and ran the following command in the Terminal: /usr/sbin/bless -mount / -firmware "MBA51_00EF_B01.scap" --recovery --verbose

Firmware preloads successfully. But when I reboot to start the installation a black screen remains during three continuous fast reboots (I guess trying to install the new firmware). Then it boots normally and no firmware downgrade happened.

Any idea why this is happening? Are there any other methods to load the BootROM, supposing that it is just being refused by "bless" for being older that the installed one?

Hope this contributes and appeals to those willing to revive the past.

----- UPDATE 30/07/19 -----

Still trying to downgrade firmware in MBA mid2012.

Normal method via 'bless' command and extracted .scap didn't work. I just get a longer black screen and no firmware update, like to someone here and here (with the same model).

I presume apple introduced the iOS policy of no-return in newer firmwares?

An alternative way would be to inject the older firmware with 'flashrom' over linux, but I don't have another MBA with original firmware from where to extract it. Someone uploaded a similar dump here. But it is for MBA2012 11" i7, mine is MBA2012 13" i5. I guess the firmware is the same, but double risk to brick it.

  • Have you tried just using macOS Recovery to install the original version of OS X that came with your Mac?. In other words, hold down the Shift-Option-⌘-R keys at startup. In your case, you may want to try the Command (⌘)-R keys, since the newest OS X installed was El Capitan. – David Anderson Jul 15 at 20:38
  • Unfortunately my SSD doesn't have the Recovery partition anymore... That's the reason why I'm trying to install the original Lion 10.7.4 from a downloaded .dmg – Domingo Jul 15 at 20:50
  • ... Thanks for the contribution David! – Domingo Jul 15 at 21:06
  • I thought you downloaded the original operation system from the internet. You should not need a recovery partition. Read the section titled If you never installed macOS Sierra 10.12.4 at the Apple website How to reinstall macOS from macOS Recovery. Again, I repeat: You should not need a Recovery partition on the internal drive. You should be able to completely erase the internal drive and reinstall the original version of OS X downloaded from the internet. – David Anderson Jul 15 at 23:06
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    Besides, you can not install Lion from an Apple purchase without first having Snow Leopard (OS X 10.6.6 to 10.6.8) installed. Read the system requirements at OS X Lion (10.7). Unfortunately in your case, you probably can not install Snow Leopard on that model Mac. It is too new. You would have to find an older Mac that is both Snow Leopard and Lion compatible. Connect the drive either internally or by using a USB shell. Next, install Snow Leopard, then upgrade to Lion. Once you have done this, you can put the drive in your 2012 Mac. – David Anderson Jul 15 at 23:24

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