Mac Pro Early 2008 - What is the power up sequence?

Discussion in 'Mac Pro' started by TommyKing, Oct 29, 2009.

  1. TommyKing macrumors newbie

    Oct 7, 2009
    I am rebuilding an Early 2008 Mac Pro. Not knowing the power sequence of the machine I have a couple of conditions that occur.that someone might be able to help diagnose what is missing. I have one E5462 CPU in socket A, socket B is empty

    1. On Power Up with all power connectors plugged in the power supply starts up for a second and switches off. The OT1 and Ot2 diag leds are lit.

    2. If the power plug next to the speaker, I think this is p1 or p2 is removed the machine powers up PSU fan runs to speed and Ram riser leds test and go out. I would call this working if I felt the CPU heat up or saw video.

    3. The board responds to nothing with the CPU removed.

    Of course I am seeing no video 8800GT card (tested is working) and Northbridge and CPU are cold.

    Do bad sensors on the heating shut the machine down.?
    Do bad fans shut the machine down.
  2. Dr.Pants macrumors 65816


    Jan 8, 2009
    Check the CPU in another machine. I am tempted to say that if your CPU isn't dead, your logic board is bad. The machine semi-powering-up kinda thows me for a loop... Does it pass POST (aka chime)?

    The "PSU on momentarily" symptom mirrors mine EXACTLY when my M2N board died a month ago, which is the reason why I think it would be the logic board.
  3. gugucom macrumors 68020


    May 21, 2009
    Munich, Germany
    Get a service manual. The 2006 manual is fairly well published in the underground. The 2008 is a bit different but not drastically though for your purposes. There is a LED row under the RAM cage in the 2006 with a test button and the manual gives some procedures how to use these particularly for CPU testing.
  4. rera09 macrumors newbie

    Oct 30, 2009
    I came to know how to check the cpu when it is not working by seeing the information in the forum thanks for all who has given the inforamtion about that.

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