G4Danny
Level 1 (8 points)
Desktops

Q: G4 MDD Power Issue

My MDD has recently been shutting down after only two or three minutes from a cold start-up. The power light comes on, the gray screen with the Apple logo appears along with the spinning wheel, but then the machine suddenly loses power as though the cord had been unplugged. These are the things I have already tried:

 

  1. Removed the PRAM battery
  2. Disconnected all peripherals except for the keyboard and monitor
  3. Tried a different power cord

 

Booting up in safe mode didn’t help. The fans are all running, the red LED lights up on the logic board, and the disk drives appear to be working. Could this be a power supply issue or a problem with the motherboard, and is there any way I can definitively pinpoint the problem without being able to start up the G4? The start up time has taken considering longer when everything was working last week—could that be a clue? I’ve owned this machine for over twelve years and have put it through its paces so I’m wondering if it’s time to retire her…

 

Thanks in advance for any help you can offer!

PowerMac, Mac OS X (10.5.8)

Posted on Aug 5, 2016 4:09 AM

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G4Danny

Q: G4 MDD Power Issue

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  • Helpful answers

  • by BDAqua,Helpful

    BDAqua BDAqua Aug 5, 2016 7:57 AM in response to G4Danny
    Level 10 (123,467 points)
    Aug 5, 2016 7:57 AM in response to G4Danny

    Hi, it sounds very much like a CPU heat issue, the Thermal paste is usually good for 5 years or so.

     

    Does it run any longer with the side door open?

  • by G4Danny,

    G4Danny G4Danny Aug 5, 2016 8:00 AM in response to BDAqua
    Level 1 (8 points)
    Desktops
    Aug 5, 2016 8:00 AM in response to BDAqua

    Hi BDAqua:

     

    "Thermal paste"?! Wow, I didn't know the CPU even had that!

     

    No, I tried booting up with the side door open and the Mac ran for the exact same amount of time before it shut down.

     

    Thanks,

     

    Dan

  • by BDAqua,Helpful

    BDAqua BDAqua Aug 5, 2016 12:05 PM in response to G4Danny
    Level 10 (123,467 points)
    Aug 5, 2016 12:05 PM in response to G4Danny

    Dan, these might help...

    The MDD is actually designed to shut down as it approaches the overheat stage. There is a temp sense circuit that controls this. Unfortunately, it doesn't give any on screen warning, nor does it do a graceful shut down. It simply dies, as if you pulled the plug

    https://www.ifixit.com/Answers/View/35536/G4+MDD+freezes+when+CPU+gets+hot+-+why

     

    http://www.xlr8yourmac.com/systems/MDD_copper_heatsink_swap/mdd_copper_heatsink_ swap.html

  • by G4Danny,

    G4Danny G4Danny Aug 5, 2016 12:07 PM in response to BDAqua
    Level 1 (8 points)
    Desktops
    Aug 5, 2016 12:07 PM in response to BDAqua

    Thanks, BDAqua. I will research the thermal paste option online and see if it's something I can tackle myself! It looks like tricky work...

     

    Dan

  • by BDAqua,

    BDAqua BDAqua Aug 5, 2016 3:36 PM in response to G4Danny
    Level 10 (123,467 points)
    Aug 5, 2016 3:36 PM in response to G4Danny

    OK, good luck & let us know if you need more help.

  • by Glen Doggett,

    Glen Doggett Glen Doggett Aug 9, 2016 12:17 PM in response to G4Danny
    Level 4 (1,863 points)
    Notebooks
    Aug 9, 2016 12:17 PM in response to G4Danny

    there are many different brands and types, like Arctic Silver, they should work about the same, this is something like the consistency of toothpaste that you put a small amount on the contact point between the CPU and the heat sink.  So you have to open up the case and remove the heatsink, wipe off the old paste with a Q-tip and apply a small amount there, two places for a dual CPU machine.  When it has not been replaced for a long time, or if you have moved the machine around or installed/removed hardware in the machine recently, it can cause some settling and shift the contact so that the heatsink can't really do the job.  Best to do that after you have worked on the machine for whatever reason.  I noticed a big difference after I replaced my power supply, basically a complete tear down and rebuild, then the fans would rev up like crazy.  But, after new thermal paste, it kept things cool without having to rev up the fans at CPU idle.