G4 MDD won't boot up.

Discussion in 'PowerPC Macs' started by Rafalski24, Aug 23, 2010.

  1. Rafalski24 macrumors regular

    Sep 27, 2009
    Denver, CO
    So my G4 MDD tower was working fine, but I turned it off last night and now it won't turn on. The light comes on when you press the power button, but then it goes off when you let go and nothing happens. The fans don't spin up and nothing makes a sound... Any ideas?

  2. raysfan81 macrumors 6502a


    Oct 6, 2009
    North Carolina
    I'm guessing you have a dead power supply, which was a fairly common issue for the MDD's. But be sure to test the current power supply to make sure it doesn't actually work. If it does then you have something else wrong. You can either buy a working PSU from eBay or somewhere or you you mod a standard ATX power supply to work with the MDD.
  3. 666sheep macrumors 68040


    Dec 7, 2009
    Plenty of :)

    Reset PMU first, if it won't help - test PSU. Is there red light on logic board (it should be, it indicates that lobo gets power from PSU)?
    Disconnect all devices from PSU and remove ATX connector from logic board. Bridge green cable with nearest black one and plug PSU to power source. If PSU fans will run, check rest of voltages on ATX connector with multimeter. http://www.outofspec.com/frankenmac/wire.shtml - if PSU will be OK - there is only one possibility: fried logic board. Examine it for physical damages, burnt elements for example.
  4. kirkbross macrumors 6502a


    Mar 6, 2007
    Los Angeles
    My Dual 867 MDD G4 won't boot. I press the power button, the power button light (and fans) come on but then the power button light quickly fades off (within one second). Then after about ten seconds the fans go into high speed mode. No startup chime, no display. Nothing.

    I reset the PMU and did all the RAM swapping tricks. Nothing. There is a little red LED on the mobo near the RAM that is on if that's good or bad(?).

    I had recently (a week ago) done a fresh Tiger install and everything was running fine. Rebooting for all the updates without incident. Then I took it to my friend's house and it booted up for a second and then I got the screen of death and it was soundly dead after that.

    It had been in storage for a couple of years unplugged... could it be as simple as the little PMU battery is dead?
  5. dante damore macrumors newbie

    Mar 15, 2011
    G4 mdd won't boot up

    I had the exact same problem.I had to constantly unplug from the wall then plug back in for the power button to work.So replaced the battery,disconnected the HD,video card and drives,NOTHING. I then purchased a refurbished PS with a year warranty and installed it,same thing,power button light was on when pressed then went right off again.The fan started spinning faster and LOUDER .

    Then after getting ready to trash it I decided to take out the dual processor board and reseat it.Guess what.... IT'S WORKING AGAIN !!!!!

    Every once in a while it will crash,guess when that happens,whenever I CLOSE THE SIDE PANEL of the case.

    I think this is a design flaw.Every time we close the case back up it needs to "Click " to lock.I've found that the logic board is jarred loose enough to make the system crash.

    When it crashes,I take a bamboo chop stick ( because it's softer than a screwdriver ) and press 4 times on the two exposed sides( all four corners ) of the logic board into the mother board.Once it reseats it starts right up with zero problems.If I close it hard it crashes but once logic board is reseated it starts right up again.

    I hope this helps
  6. kirkbross macrumors 6502a


    Mar 6, 2007
    Los Angeles
    Thanks for your reply... I actually did reseat the CPU daughter card. Cleaned mounds of dust from under the logic board and still nothing.

    But... I just bought a replacement CPU daughter card off eBay for $9.99. What you are describing could still be the same problem, basically no CPU found at boot -- in your case, mis-seated, in my case fried (hopefully).

    It's amazing a CPU is only ten bucks while a refurbished PSU is over a hundred. I wanted to try the CPU first. Next, logic board then lastly PSU.
  7. hansolo669 macrumors regular

    Oct 5, 2009
    now just my two cents, but i dont think replaceing the cpu card will fix it (it might it might) just a few trouble shooting ideas:
    did you remove ALL cards (yes even the vid card) and attempt to boot?
    did you remove all harddrives except the boot drive and attempt to boot (with only the vid card)?
    did you try unplugging the comp pressing the power buttion for 10sec then plugging back in?
    did you try replaceing the PMU battery?
    did you try a boot without the PMU battery?
    did you try removeing all harddrives and booting to see what happend?
    does the psu fan spin up? (hold down the noisy main fan with a pen or something and see if the psu fans spinn up)

    personally im thinking dead or dying logic board, or dead/dying psu...but thats just my 2 cents

    **edit** where did you find that dual 867cpu card for $10? link? :p
  8. bizzle macrumors 6502a

    Jun 29, 2008
    Check to make sure all other power connectors are secure. I've had issues with one of mine where one was loose and the machine had the same symptom.

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