Weird RAM issue, 2015 5k

Discussion in 'iMac' started by makrom, Mar 25, 2016.

  1. makrom macrumors regular

    Nov 4, 2015
    I upgraded my RAM with 4 8GB Kingston HyperX 2133MHz (11-12-13) and I get memory errors with Rember. I'm also getting somewhat frequent application and OS X crashes that I neither get on my rMBP nor before the RAM upgrade.
    Rember gave me the following error:
    FAILURE! Data mismatch at local BUFA address 0x0000000496ca2ec8, BUFB address 0x000000082cd426c8
    BUFA Data: 0x7edb584effe57bd9, BUFB Data: 0x7edb584effe57bf9

    Since I couldn't match this memory address to a RAM bank, I tried to test the RAM modules 2 by 2 until I could isolate the culprit.
    But here's the weird thing: The memory issues only occur when I use all 4 modules. When I use any 2, the tests never failed. I tried them in bank 1 and 3 or 2 and 4, but they work fine regardless.

    So basically I can currently use my iMac with 16GB, no matter which modules or banks I am using, but I can't use all 4 at once.
    Is there any way to diagnose what could be the cause for that?
  2. maflynn Moderator


    Staff Member

    May 3, 2009
    Return the memory and try a different manufacturer.
  3. makrom thread starter macrumors regular

    Nov 4, 2015
    Well I guess that might work, but returning a non defective product would mean additional costs. Also, couldn't it be a mainboard issue as well?
    Another problem is that there aren't many lv 2133 alternatives available and I went with these since many people here reported them to be working fine in their late 2015 5k iMacs.
  4. Fishrrman macrumors G5


    Feb 20, 2009
    As maflynn said above, you have RAM that's either defective or incompatible with the factory-installed RAM.

    You can return it, or -- live with the crashes.

    Your choice.

    I'd suggest Crucial RAM, or perhaps from this source, which has done well by me with other Macs:
  5. makrom thread starter macrumors regular

    Nov 4, 2015
    I'm sorry if I phrased it poorly, I don't use it together with the RAM my iMac came with as it only has 4 banks, also the stock RAM only runs at 1866MHz.
    And this particular type of RAM has been reported as working well in these iMac models so I don't think it's incompatible per se. Is there even such a thing as RAM incompatibility that only occurs when using 4 instead of 2 modules?
    To ask in a more specific manner, is there any way to determine which RAM module might be defective, as in matching a memory address to a module? Or is there an effective way to test whether my mainboard might have issues with using 4 modules?

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