Bottom Riser Red LED light on! RAM use to work now it doesn't..

Discussion in 'Mac Pro' started by swingline, Mar 10, 2008.

  1. swingline macrumors member

    Aug 9, 2005
    I just installed 4x1gb OWC ram onto my top riser, adding onto my previous 2x512(dimm 1&2) + 2x1gb setup (which is now on my bottom riser). My previous setup had no problems and OSX detected the ram just fine but now with my previous setup on the bottom riser, OSX only detects the top riser with the new OWC 4x1gb ram. My former setup now displays a red LED light on the bottom riser.
    It does seem to detect all RAM when the risers are switched around but what did I do wrong to make it not work the other way?
  2. djjclark macrumors regular

    Feb 17, 2008
    It sounds like you never had memory in the bottom riser? If so, I would consider the chance your riser is bad. My bottom riser had a lit red led for the 2nd dimm no matter what memory I put in and Apple replaced the card for me and all is well now. If you had been using it I would look around here for the configuration guide to make sure of proper configuration. Also try reseating everything.
  3. pprior macrumors 65816

    Aug 1, 2007
    Reseat everything. Swap ram risers and see if the different ram (same riser) is bad. Most likely it's a bad insertion. I suppose you could have zapped a module or riser when removing.
  4. WardC macrumors 68030


    Oct 17, 2007
    Fort Worth, TX
    RAM is supposed to be installed in matching pairs as detailed in the manual under "Installing memory in the Mac Pro" it shows you which slots are to be installed in pairs (you install pairs as, one in upper and one in lower riser) You don't fill up one riser and then use the other riser.

    From what I understand, the Mac Pro WILL recognize any memory you install in there, in any riser as long as it's the right kind of RAM, but the matched pairs are supposed to be installed in such a way for performance benefits.

    Anyways, it would be best to consult the manual:

    Pages 43-46

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