Mac Pro 2008, 3,1 not turning on, being weird

Discussion in 'Mac Pro' started by tarascrysix, May 3, 2015.

  1. tarascrysix macrumors newbie

    May 2, 2015
    I've got a Mac Pro 3,1 2008 model running a 2 x dual core with a cuda card & 16 gb of ram. Recently it has been working perfectly fine, but yesterday when i got back home and switched it on, the CPU Fan started to run really fast and no chime or anything. I immediately got worried and held on the power button until it switched off. After that it doesn't switch on anymore.

    I've gone through the manual and these are my observations:

    When I plug in the AC power, the power-led turns on then off. Also the OT A & OT B LED turns on and off at the same time. There is trickle power. Nothing else occurs. So my presumption is that the power supply does bring power in but is not regulated.

    When I plug the AC power out, the power-led turns on and off (very quickly). No other LEDs flash or anything. Something is discharging?

    If i hold on the power button, and plug in the AC power, and keep holding on the power button for maybe 10 seconds, the power-led is constantly on, OT A & B is constantly on. No fans are running, no sound, it's just dead except for the LEDs.

    If I refer to the manual, following the symptoms of having trickle power, no power-on, OT A & OT B turning on & off immediately, it means that I have either an incorrect power-cable connection or a bad power supply.

    I doubt the incorrect connection as i've not fiddled with the cables beforehand. The bad power supply could be the probably cause. I've replaced the battery, stripped the desktop down to only the logic board & the power supply, but still have the same problem.

    So its either the power supply or the logic board. So maybe someone out here had the same problem and found a solution?

    I'm leaning towards the power supply. I'm in sydney, australia and i've no idea where to get a spare power supply. Ebay only shows up with one item and it's for the 2006 model not 2008 model. Are there third party power supplies that will work on the 2008 model?

    thanks guys!


    I also forgot to mention that after the plug is taken out, the power-on LED flashes, then after a few seconds it flashes again
  2. CanadaMaple macrumors member

    May 1, 2015
    Immediately I would assume the PSU. Possibly someone else can give some input here.

    Have you added/removed anything recently (upgrade) wise?

  3. tarascrysix thread starter macrumors newbie

    May 2, 2015
    Hey, no I haven't upgraded anything it's been running as it is for two months, I did pick it up second-hand but the previous owner didn't have any problems with it either.
  4. bax2003 macrumors 6502a


    Dec 25, 2011
    2 x Dual Core ?

    Mac Pro Early 2008 came with single Quad Core 2.8 or 2 x Quad Core 2.8, 3.0 or 3.2.

    I don´t even know that there are Dual Core Harpertown CPUs :confused:
  5. tarascrysix thread starter macrumors newbie

    May 2, 2015

    Sorry I meant 2 x Quad core, 2.8 Ghz i believe.
  6. bax2003 macrumors 6502a


    Dec 25, 2011
    CPU A OT = CPU A is over temperature, and the same for B. I don't like when Mac Pro logic board points out to that, because in many cases it does not have anything with CPUs overheating.

    - try resetting the SMC
    - verify proper processor heat sink installation
    - verify all thermal sensors and their cables are properly connected

    From Service Manual: If both overtemp LEDs come on immediately when the computer is turned on, a faulty power supply could be one cause of this behavior. Replace power supply.
  7. nigelbb macrumors 65816

    Dec 22, 2012
    I had the same problem with my 2008 3,1 & as I am in the UK I also had trouble sourcing a power supply. I was in the happy situation of having two identical Mac Pros so could swap over power supplies & confirm that was the fault before I bought a replacement.

    I checked on eBay & there are a few power supplies for sale even a new one from the US. The problem will be cost of shipping to Australia however if you could confirm that it really is the power supply at fault then it could be worthwhile.

    If you have no other power supply to swap over to confirm the fault then it would be worthwhile taking the Mac Pro to an Authorise Apple Repair shop & getting them to confirm the problem & give an estimate for repair. The problem with ordering a used power supply from eBay is that it could also fail in a month or two & you would be back at square one.

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