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Mid 2012 model, A1278 / 2.5 GHz i5 or 2.9 GHz i7 processor.

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Booting up to a no entry sign... OCLP?

I have a 2012 MBP 13" here that boots upo to a no entry sign, we have tested with 3 HDD Cables and swapped a known good SSD with a clean install of Catalina on it, to no avail. We can safely rule out a cable issue, SSD, HDD, or RAM as all are good. I cannot get into boot options or diagnostics either so I am thinking this may have been patched with OCLP before as the previous owner has kept the SSD from it and they don't respond to any questions asked (They don't know)..... If my assumption is incorrect, any ideas what we need to look into as I have tried just about every other option....?

If your Mac starts up to a circle with a line through it

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Are you able to boot up under a clean supported macOS? Then modify this external with Open Core?

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@danj Already stated a clean installed SSD..... Zero options at boot also..... If it is indeed OCLP related then a real headache to detect which OS it was patched to....But yes, needs to get back to the last working system whatever that was, then remove the post root patches, then wipe and install HS or Catalina anew.....Maybe HS to Catalina update will get me the 10.15.8 installer IF it exists :D

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@livfe - re-read >> not the Internal >> we need to do the External.

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@danj When I connect an external drive with an installer or a supported system nothing is showing up, it just goes directly to the no entry sign.... I see no reason why the option key maybe faulty (Possible), no external KB to try with. Later today I will see what I can muster up and get this running again......

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If clean bootable drive (High Sierra in this case and no other partitions) is unable to boot externally (with no internal drive present) just on its own or even if you try using the startup Manager via the Option Key won't boot with out the prohibitory Icon. The Low level boot loader held in the systems firmware is corrupted somehow.

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@danj Which is fixable by what method? BIOS Chip swap? SMC Reflash? Game Over?

The external drive I tried actually has 4 or 5 partitions, each containing a different OS From Lion, El Captain, High Sierra, Catalina, Monterey.... I believe these were the ones that included a firmware update from their predecessors.

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@livfe - Cloning a good chip and altering the systems values to this system on a fresh chip.

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@danj Taking a BIOS chip from another identical model and transplanting it then.... we can do that 😁

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@livfe - That also works

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@danj OK Great, we will swap one over before assembly and hopefully it is fixed, Thanks! :)

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livfe will be eternally grateful.
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