G5 2.5Ghz start up issue

Discussion in 'PowerPC Macs' started by mark8, Jan 23, 2016.

  1. mark8, Jan 23, 2016
    Last edited: Jan 23, 2016

    mark8 macrumors member

    mark8

    Joined:
    Nov 29, 2010
    Location:
    WNY
    #1
    hello
    tried starting my Powermac G5 dual 2,5ghz mac. I had given up on this for almost a year.
    Here's what is going going on and what I tried. I rebuilt the LCS with new O rings and new coolant. I tried booting with ram and video card out but still got the same result. The white power button LED does not stay lit. It boots with no chime, and the fans eventually ramp up after awhile. The battery is at 3.6V. Tried the pmu reset. I tried a different power supply and another LCS/cpu combo as well. I may try a different logic board, but would rather not. Went through this and other forums and tried other tests with the same result. There are no red LED's lit up on the logic board. Any thoughts?
     
  2. eyoungren macrumors P6

    eyoungren

    Joined:
    Aug 31, 2011
    Location:
    Phoenix • 85037
    #2
    If you've tried everything else except the one thing you're dreading and it hasn't work it would seem the only thing left to try is that.

    I'd try a new logicboard.
     
  3. MacCubed macrumors 68000

    MacCubed

    Joined:
    Apr 26, 2014
    Location:
    Florida
    #3
    Its either the CPU, LB, or PSU. I think it's most likely the PSU, but if the LCS had leaked before, it could be the CPU or LB due to damage from the coolant. Since you said that you tried a different PSU and CPU, I say LB
     
  4. rawweb macrumors 6502a

    rawweb

    Joined:
    Aug 7, 2015
    #4
    Are you absolutely sure the CPU assembly was installed/seated correctly? Might be worth taking it back apart and verifying the CPU cards are lined up precisely and then taking a magnifying glass and insuring you didn't accidentally bend any of the small pins on the CPU cards or logic board. Then follow the apple service guide for re-installation to the letter. To me, what you describe almost sounds like the processors aren't seated correct, I had something similar happen during one of my many teardown operations on my quad.
     
  5. mark8 thread starter macrumors member

    mark8

    Joined:
    Nov 29, 2010
    Location:
    WNY
    #5
    all sound advice, will investigate the next chance i get. thank you all
     
  6. Hack5190 macrumors 6502a

    Hack5190

    Joined:
    Oct 21, 2015
    Location:
    Stuck on Earth in the USA
    #6
    I have a dual 1.8 that is as unpredictable as a rat in a cheese store. At boot it often acts like you've described. Removing the A/C, 3.6 battery, resetting the PRAM and pressing the power button 2 or 3 times will often 'revive' it.

    As others have suggested there are many potential causes. After going through a long list and all the Apple service & test disks, the motherboard is always the suspect.

    Good luck.
     
  7. mark8 thread starter macrumors member

    mark8

    Joined:
    Nov 29, 2010
    Location:
    WNY
    #7
    WHAT'S THE A/C?
    THX
     
  8. MagicBoy macrumors 68040

    MagicBoy

    Joined:
    May 28, 2006
    Location:
    Manchester, UK
    #8
    I think in this context it means the mains power.
     
  9. Hack5190 macrumors 6502a

    Hack5190

    Joined:
    Oct 21, 2015
    Location:
    Stuck on Earth in the USA
    #9
    Correct!

    A/C = Alternating Current ;)
     
  10. MagicBoy macrumors 68040

    MagicBoy

    Joined:
    May 28, 2006
    Location:
    Manchester, UK
    #10
    I've never seen it expressed with a slash in before. When I see A/C I immediately think Air Conditioning...
     
  11. Hack5190 macrumors 6502a

    Hack5190

    Joined:
    Oct 21, 2015
    Location:
    Stuck on Earth in the USA
    #11
    You raise a valid point - like you I also use A/C to abbreviate air conditioning. Time to make a change, thanks for pointing that out.
     
  12. mark8, Mar 15, 2016
    Last edited: Mar 25, 2016

    mark8 thread starter macrumors member

    mark8

    Joined:
    Nov 29, 2010
    Location:
    WNY
    #12
    Well I bit the bullet and swapped out the Logic Board and I got a boot chime...yay Progress!
    The weird thing is when i plug it in, the hard drive starts up without pushing the power button. I still get a boot chime(when i do push it) and it tries to start. Never had the HD thing before. I have been taken these apart for a few years now, and never ran across this. Still logic board issue?
     

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