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Changed the motherboard/logic board of a MBP 13" 2014 model. After the operation it just shows a blinking question mark when starting. I can however boot it from a High Sierra USB drive and when it logs in there it asks for the password to unlock the internal SSD, showing that it can read the SSD.

I can also mount the SSD in a MBA 13" 2013 that I have and it will boot from the SSD, like it happens with FileVault encrypted disk, it boots and the log in screen appears very quickly.

I have tried SMC reset and NVRAM reset on the MBP but no luck. I don't understand why it won't boot to the login screen with the encrypted SSD on the MPB? Is there something I can do about it?

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It's kind of a work around but why not try decrypting it with the MBA, then seeing if the MBP boots it. If it does, then re-encrypt it and see if that works.

  • Thanks, you are probably right that that is the only way. It's just weird that it refuses to boot with the new motherboard. my little problem is that the owner doesn't seem to remember the login password, and he is in another town. Now IF MBP had booted fine it wouldn't have been my problem, but I can't ship him an MBP with a blinking question mark on startup... – Lars A. Gundersen Apr 28 '18 at 16:35
  • Always have the customers give you the password if they're not going to be present during the repair. – l008com Apr 29 '18 at 6:43
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I think the boot volume is corrupted, try following the instructions in the article:

If a flashing question mark appears when you start your Mac

Boot from the recovery USB and select reselect your startup disk.

  • The SSD boots fine in another Mac, as mentioned in the question, so that is not it. – Lars A. Gundersen Apr 28 '18 at 16:32
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I have since realised the answer, which is simply that motherboards gotten from another source might have not before run the newer version of MacOS that you used on the MacBook before, therefore it needs a firmware upgrade to be used.

You can upgrade the firmware by booting it from an older version of macOS then do an upgrade to the version of MacOS you are trying to run on any spare disk or partition. As lng as you are doing the upgrade while booting on the motherbaord youwant to use, it will get the necessecary firmware upgrade in the process, which will allow you to boot from the FileVault encrypted disk you wanted to boot from in the first place.

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