My Mac Pro 3, 1 began rebooting randomly one day and the next it wouldn't come back on. Pushing the power button results in a fan clicking in to life for half a second and then all power is lost. The RAM board LEDs and Diagnostic LEDs OT A and OT B both flash momentarily. When the diagnostic button is pressed on the logic board the Trickle Power LED lights orange.

All my troubleshooting led me to believe the PSU was borked. But when on the phone to Apple support, around a week later, I tried one last time to turn it on and it roared in to life. It stayed on for a few days and I backed everything up. It hadn't been off at all, I updated from 10.10.1 to 10.10.2 and rebooted. No issue. I shut it down.

At 8am the next day I woke up to the computer trying to start, and I remembered that before the initial problems I had set it to wake at that time. But then it clicked off and it's been refusing to start ever since.

Apple support (over the phone) say they don't think it's the PSU as it wouldn't have started working again. What could it be? Could it be the automatic wake?

I have tried removing the memory boards and every other component one by one without any luck.


I'm not getting to any screen, grey screen, unhappy mac face etc.

Also, this, from the service manual was why I decided it was a PSU issue in the first place...

"If both overtemp (OT) LEDs come on immediately when the computer is turned on, a faulty power supply could be one cause of this behavior. Replace power supply."

  • tried SMC reset? power off, unplug from mains, wait 15s, plug in, wait 5s, try again. Mine once did just that & the reset was all it took to get it up again.
    – Tetsujin
    Feb 22, 2015 at 8:46
  • I think so. Do those numbers count? I have had it unplugged as I have tried different power cords.
    – Mark
    Feb 22, 2015 at 8:48
  • the wait times are what it says on the apple site, idk how exact you need to be, tbh.
    – Tetsujin
    Feb 22, 2015 at 8:48
  • I'm trying to recall what recent changes I'd made when mine did it - I'm thinking it was when my old 8800 died & I put a 5770 in.
    – Tetsujin
    Feb 22, 2015 at 8:49
  • 1
    Graphics cards; the stock NVidia & the Apple ATI replacement. Something a 3,1 owner would already know, so I didn't feel the need to flesh it out just in comments.
    – Tetsujin
    Feb 22, 2015 at 9:52

2 Answers 2


I ended up solving this. I had installed a SSD, and connected it to the hidden sata port. It worked for a couple of months. Then one day I had this issue. I took the ssd out and installed OSX on the first drive bay and it booted! I'm guessing the fan chassis must have been snug against the connector or otherwise some dust was causing grief. In any case. I'm glad I didn't pay an exorbitant fee for the rare aftermarket PSUs.


Just found this again whilst searching for something else.

Having since experienced something very similar since with a 3,1 I'd definitely say it's worth a couple of bucks for a new PRAM battery, standard CR2032 you can get from any supermarket these days.

I chased mine for days thinking all sorts was wrong - PSU, bad RAM, all kinds of errors coming up in AHT - before changing the battery, & everything has worked perfectly ever since.

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