Power Mac G5 Quad overheating - LCS problem (photo)

Discussion in 'PowerPC Macs' started by Tryp, Dec 4, 2012.

  1. Tryp macrumors newbie

    Dec 4, 2012
    Hi to one and all,

    I purchased a Power Mac G5 Quad Core (late 2005) last month for my small business, as I was in need of some firepower to out-muscle my old computer. I do music production and things were starting to slow down when adding in plug-ins. Unfortunately I was ignorant, and trusted a failing auction company, spending £350 on this very large paperweight which showed up to my door full of dust and unable to startup.

    To cut a long story short, I used canned air and curiosity to clean the whole thing out, and managed to get it started up for the first time.

    However, it often shut back down on startup and when I checked the stats, CPU B Diodes 1 & 2 were running around 89/91* whilst CPU A Diodes were running around 33*, which are where I believe they should be.


    Why does one CPU pair run so hot whilst the other runs so low? It seems as if either the workload is being routed solely to the CPU B pair, or that the Liquid Cooling System (LCS as we know it), is only cooling CPU A very well and not cooling CPU B very well at all.
    This sounds like a thermal conduction problem, leading to either a malfunctioning LCS or even poorly applied/dissolved thermal paste. (I've heard the thermal paste used was highly toxic so any honest answers regarding changing this, please consider safety ;))

    There is hard green stuff around the tube connections of the LCS and no sign of any leakage, this seems like glue but if anyone has any other proven suggestions? How do I check the LCS is pumping and working well? Or that it is full with liquid?


    Thank you in advance for any time taken to read or help, I've trawled every forum out there and can't find a specific answer to this problem.

  2. nickjf20 macrumors member

    Jan 2, 2009
    There's two separate loops i.e. one pump and rad for each processor

    On one the pump is broken / the system has leaked.

    At least you know the processors not fried (yet) :p
  3. Tryp thread starter macrumors newbie

    Dec 4, 2012
    Hi Nick, thanks for the response,

    Damn.... I'm going to have to read that whole hideously formatted thread on www.xlr8yourmac.com aren't I.....?

    Do you know if the hard green stuff around the tubes in the picture is dried coolant or glue used to stop leaks? It doesn't look very standard. I reckon it'll probably make it pretty hard to get the tubes free to start the DIY too.

    Also do you know which is for CPU A and which for CPU B, top and bottom? I'm thinking why mess with the system working well, and I'll just have a bash at the overheating CPU B.

    Thanks again!
  4. jbarley macrumors 68040


    Jul 1, 2006
    Vancouver Island
    Looking at your photo I notice a hint of green coating almost everything, this might be a sign of coolant leaking.
  5. drorpheus macrumors regular

    Nov 20, 2010
    Tryp, that yellow stuff is epoxy glue to seal it shut. over by the pump it looks green because its translucent yellow over black. Its not leaking at those points in the picture. It may have clogged on the bottom cpu and needs to be cleared out, in the radiator/cooling block underneath.

    They used the epoxy as a fix to ensure no leaks, sadly overtime the coolant crystalizes and clogs, like a car, without a flush.

    CPU0 or CPU A is the top one, CPU1 or CPU B is the bottom one.
  6. Tryp thread starter macrumors newbie

    Dec 4, 2012
    Thanks drorpheus, that confirms my earlier suspicion. Can I ask if it was practise at Apple to apply this epoxy glue or does this look like a user repair? I've seen a few photos of other LCS units, and the lower port on the left of each of the two lines looks like a screw cap, whereas on mine it looks like a glued end of some rubber tubing.
    It sounds like I'll have to get my hands dirty on this one, but anything's worth a shot. It would still be a serious computer if I could fix this one problem.

    @Jbarley - I think this must be the hue on my cameraphone, it's actually a horrible, fine, sandy dust which covered almost everything inside when I received it! This photo was before I plucked up the courage to start unscrewing everything and getting in with the air cannisters. Which worked to a certain degree!

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