Mac Mini (Late 2012) - POST Chime Boot Loop

Discussion in 'Mac mini' started by RyanXM, Mar 8, 2018.

  1. RyanXM, Mar 8, 2018
    Last edited: Mar 9, 2018

    RyanXM macrumors 6502

    RyanXM

    Joined:
    Jul 7, 2012
    Location:
    DFW, TX
    #1
    I had a family member call me today and asked if I knew how to resolve a POST chime boot loop. They attempted the usual.

    PRAM Reset - didn't resolve anything.
    SMC Reset - didn't resolve anything.
    Option Boot - didn't resolve anything.
    Target Disk Mode - doesn't not function.

    Able to get display to show a blank white screen. Power button does power device on and off. Unit does show rapid flashing power LED when power button is held for longer than 5 seconds.

    My understanding is that EFI was put into an update mode and because it can no longer find the update, either from external device or internal HDD, that it will just continue to POST chime and boot loop until the update is found and flashed.

    Any help is greatly appreciated!

    Ryan
     
  2. ActionableMango macrumors G3

    ActionableMango

    Joined:
    Sep 21, 2010
    #2
    Is the flashing in an "SOS" pattern? Three quick, three slow, three quick?

    If so, there was a failed attempt at a firmware update and you will have to make and use a firmware restoration CD connected via an external optical drive. Or if you don't have the means to do that, take it in to Apple.
     
  3. RyanXM thread starter macrumors 6502

    RyanXM

    Joined:
    Jul 7, 2012
    Location:
    DFW, TX
    #3
    It seems as though that is the issue. I don't have the Mini in front of me.

    As far as a firmware restoration CD, Apple never produced one for the Mid 2011 or Late 2012 Mac mini. If you know of a way to create one, please let know. I have an external SuperDrive.
     
  4. ActionableMango macrumors G3

    ActionableMango

    Joined:
    Sep 21, 2010
    #4
    No I don't. If you can't find the CD for that model and it is flashing SOS then the only thing I can think of is to bring it in to Apple.

    It should be possible to physically short two pins that would prevent the computer from reading the bad ROM, and thus using a failsafe instead. Then you unshort the pins after bootup and do the Mac Mini 2012 v1.8 firmware flash. But this is a very very long shot and I would only try this if I've given up on the computer and accepted it as a loss.
     
  5. RyanXM thread starter macrumors 6502

    RyanXM

    Joined:
    Jul 7, 2012
    Location:
    DFW, TX
    #5
    At this point, I'm willing to give it a shot. Do you know what pins?
     
  6. ActionableMango, Mar 12, 2018
    Last edited: Mar 12, 2018

    ActionableMango macrumors G3

    ActionableMango

    Joined:
    Sep 21, 2010
    #6
    I honestly don't think it is feasible and I'd prefer you go to Apple. But if you've truly written off the computer and are willing to go for a long shot:

    The ROM chip is a standard 8-pin SPI. It looks something like this:

    [​IMG]

    I don't know where it is, so you'll have to look around for it or PM someone else who has already found it. According to this thread where someone found it, it has model number MX25L6406E on it.

    I found a picture of the pinout for this chip. I cannot verify if it is accurate or not:

    upload_2018-3-12_10-15-11.png


    In a nutshell, what you need to do is short ground pin (black) to VCC pin (red) prior to startup. This shorts the power, preventing the ROM from being read. (Get your bearing for the pins by finding the circular indent near the corner, which is circled in the above image.)

    Being unable to read the ROM should hopefully cause the computer to use the failsafe ROM instead. Then after bootup, remove the short prior to flashing so that the communication is enabled again. Run Apple's firmware updater.

    Hopefully
    Apple's downloadable Mac Mini 2012 firmware upgrader won't mind overwriting a corrupt ROM, but I worry that it has safeguards in place that maybe it won't proceed unless it can verify the existing ROM is an older version.

    I have no idea how you're going to do this in a mac mini. Somehow you'll have to boot it up while the case is open so that you've got the short in place and can remove the short prior to flashing.

    Here are much longer instructions for recovering from a bad flash on a GPU. The principles are the same.

    Of course, this is all assuming that your problem is a bad flash in the first place, which would be based on the SOS pattern LED flashing.

    Like I said, very long shot.
     
  7. RyanXM thread starter macrumors 6502

    RyanXM

    Joined:
    Jul 7, 2012
    Location:
    DFW, TX
    #7
    Tried that unit will not boot. It seems as though there isn't a failsafe ROM available. I'll get it sent off to my component level repair guy and have him solder on a new BIOS chip. That should resolve the issue. I'm not paying $360 for a new board from Apple.
     
  8. ActionableMango macrumors G3

    ActionableMango

    Joined:
    Sep 21, 2010
    #8
    He can get a new chip with a proper 2012 Mac Mini firmware preloaded on it? Otherwise, I don't see how a new chip will help.
     
  9. RyanXM thread starter macrumors 6502

    RyanXM

    Joined:
    Jul 7, 2012
    Location:
    DFW, TX
    #9
    That he can. There are tools to flash the chip, but I just let him do that work for me.
     

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8 March 8, 2018