Mac Pro (early 2008): RAM count wrong & clocking issues for no apparent reasons

Discussion in 'Mac Pro' started by Ignazius, Oct 4, 2013.

  1. Ignazius macrumors newbie

    Oct 4, 2013
    Hello, I am new to this forum and kindly ask for your opinion and/or advice on the following issue:

    I am running a Mac Pro, 2 x 2.8 GHz quad core Intel Xeon (early 2008), (MacPro3,1) and recently changed RAM. I purchased the prescribed type of RAM boards ....DDR2 FB-DIMM 800 MHZ. 8 x 2 Gb Boards - so the thing should sport 16 Gb in total, using all available slots.

    However, it is not so:

    Riser B usually shows slots 3 & 4 as being empty. On some days slot 4 only is indicated as empty, slots 1, 2, 3 are indicated properly as occupied.

    So, usually I am seeing 12 Gb of RAM, on a good day 14 Gb, but never 16 Gb as it should be.

    At any time the clocking is down to 667 MHz instead of 800 MHz.

    I experimented a lot - changed the RAM boards around, put them in different combinations and so on. You know the ropes… All RAM boards are in good order, but I am still getting 12 GB to work with.

    Two observations strike me in particular:

    1.)When removing riser B entirely, just using riser A with any combination of four RAM boards, it shows the right specs….clock-rate is correct, and so on…all is fine.

    2.) Using both risers and putting two of my old, original (Mac) 1 GB boards in slots 3 & 4 on riser B in addition to two of the new 2 Gb boards in slots 1 & 2, then the machine shows the correct amount amount of given RAM, but the clock-rate is again wrong. Although all of the boards are definitely 800 MHz boards. What gives??

    Also, there is this red light on riser B…occasionally, sometimes not.

    Could the riser board itself be faulty?

    If anyone has any experience with this annoying behaviour - I would really appreciate your input.

  2. pastrychef macrumors 601


    Sep 15, 2006
    New York City, NY
    Maybe you can try cleaning the contacts on the riser cards. This can be done using a pencil eraser. Be sure to remove the debris left behind by the eraser.

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