This procedure is for those who have reformatted their firmware probably following the instructions from Apple on what to do prior to selling or transferring your computer. Possibly you replaced your mother board and the technician did not set the serial number. Subsequently you find that you are unable to create apple IDs (With a claim that the maximum limit have been created) login to your apple ID account, or icloud account because OS X El Capitan and later are checking your system serial number which should be stored in the firmware. If under the Apple menu about dialog you find that your serial number is ‘Unavailable’ then this procedure is for you.
You can find your serial number with a loupe or good magnifying glass (If your eyes are still those of an under 40) in micro print on the back of your device. See the list of links lower in the page here for the location by model. Preferably take a snapshot of your about dialog before reformatting the machine, but that would take some foresight. Don’t spend time chasing down your receipt or invoice as only later sales have this on the paperwork. Look for the number physically on the back of the machine. Any circular letters are zero characters. Write the number down in clear unambiguous print.
Download an apple tool called the “Blank Board Serializer” from the non apple link here. It is a zip file which will expand automatically as a folder. Is the dmg image from this folder which you will use to create a USB thumb drive that can be used to boot your machine into a utility.
Based on a method posted on MacRumors here and updated for El Capitan below create a USB thumb drive which was able to boot by holding down the option key during OS X El Capitan reboot. There are many sets of instructions online which use dd, but this process is simpler and doesn’t require use of the command line. The diskutil burn option is no longer in the graphical user interface of OS X El Capitan making the solution below preferable.
- Open Applications Folder/Utilities/Disk Utility
- Plug in a blank USB, or at least one you are willing to wipe
- Format USB to Mac Extended (Journaled)
- This will create a default partition on the USB of GUID
- Unmount created Partition (Do not eject it. Use the Unmount button at the top of the screen.)
- Open the disk image from the File menu of the disk utility.
- Select the blank USB on the external list. By default called ‘Untitled’.
- Select Restore.. from the Edit menu of the disk utility.
- Select restore from: Blank Board Serializer
- Once the above is completed