I got a Mac Pro early 2008 2x 2.8 quad-core for 12 years now. A few weeks ago, it stopped booting after 5 seconds. I restarted it and it was ok. But the problem came more and more often the next days, and today it just doesn't boot anymore. It stops after only 2 seconds. I've noticed that the CPU LEDS 5 & 6 flash in sync one time at the very end, when the fans stop with a last 'clic'. I tried everything I could do before posting this question, I mean unplug all hardwares, cleaning, and I followed the very complete answer from @monomeeth Boot fail diagnosis

When I press the DIAG_LED, I got only the LED 2 on. So I don't know if the problem comes from the Logic Board or from the PSU... hope it's not both :(

I'm about to order a used PSU for trying, but I'd like to be sure. The noob question is : if it's a PSU trouble, why the computer was able to start correctly sometimes ?

Thanks in advance for your precious help !

  • Did you change the PRAM battery yet? That's first. You'd be amazed at how much random sh** happens if that's dead. Mine [from your linked question] turned out to be a dead RAM riser board. Removed it worked fine [I had some odd results as I also had one dodgy RAM stick which confused things] Unfortunately since then the mobo died too, so I got a 'new' machine entirely, same model, fewer hours. Mine had been 24/7/365 for over 10 years.
    – Tetsujin
    Commented Dec 4, 2019 at 17:21
  • You mean the CR2032 ? Yes brand new. I've also tried to remove the 2 risers and exchanged them. It would be crazy if they are both dead at the same time, but not impossible in fact...
    – user355168
    Commented Dec 4, 2019 at 17:31
  • reduce to one RAM stick in each & test individually. It still could be PSU or mobo… but I'd eliminate the 'easy bits' first. If you can't self-diagnose easily, I'd compare prices of individual PSU & mobo against that of a full 'new' machine.
    – Tetsujin
    Commented Dec 4, 2019 at 17:45
  • Did it without success... you're right about a new machine, but the PSU I found is 50€ only, so I could give it a chance :)
    – user355168
    Commented Dec 4, 2019 at 18:00
  • OK, that's a reasonable price - but I'd still weigh it against being able to get a whole replacement machine for €250 - especially if it turns out not to be that, so next would be the mobo… ad infinitum. I fought mine on & off for a year but eventually gave in. Now I have one for 'spares'… though I still don't know which bit finally failed ;)
    – Tetsujin
    Commented Dec 4, 2019 at 18:11

1 Answer 1


The new PSU did the job ! The EFI led is still off but everything works fine now :)

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