When I turn it on, it shows the Apple logo and starts loading up to about 50%, then the screen turns black. Running the hardware test shows this:

Alert! Apple Hardware test has detected an error. 

4MEM/61/40000000: 0x79d53990

Hardware test Error

Running the system file diagnostics shows this:

file system is OK

What error is that? How can it be fixed? I don’t have a back up and can't risk losing my data.

  • Firstly, welcome to Ask Different! :) Can I ask which 15" mid-2012 MBP you have? More specifically, is it the Retina model or the non-Retina model? – Monomeeth Aug 27 '18 at 6:13
  • You should call Apple Care or initiate a Chat on Apple Support website and mention the error code. It will help them to understand the issue and explain to you. – Pratik Aug 27 '18 at 8:41
  • I don’t have a back up and can't risk losing my data. I can't stress this enough: You are risking your data every day you don't back it up. See this post under the section "A Word About Backing up Your Data." That said, the 2012 MBP can have the HDD removed. Even if your logic board fails you can save your data - chalk this up to "lessons learned" and get a back up going. – Allan Aug 27 '18 at 13:47
  • Apple Technote HT203747, Apple Diagnostics: Reference codes, list the error codes. Unfortunately it does not list yours. Derp... – user83961 Feb 17 '19 at 14:04

The error code indicates that the Apple Hardware Test tested your RAM-modules and found a problem with at least one memory module. In order to solve this you'll need to have the RAM module replaced (i.e. hardware repair).

If you have the 15" MacBook Pro (mid-2012, non-retina), you can buy a new RAM module yourself and replace it fairly easily.

If you have the 15" Retina MacBook Pro (mid-2012) the RAM module is soldered on the logic board and not easily replaceable. In this case, contact Apple or a repair shop for help.

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