Our Mac Pro A1186 which was turned off for a while during Covid, now does not turn on anymore.

When pressing the power button, it makes a clicking sound, then 3 seconds later another one, and simply nothing happens. No fans spin up, no power light, nothing.

Diagnostic LEDs:

(A) both LED 5 & 6 flash once when the power cable is connected, no other LEDs light up

(B) when the DIAG_ LED button is pressed, only LED 2 lights up as is yellow, indicating that trickle voltage is present

My questions:

(1) would this mean that the power supply has failed ? Reading the service manual, this seems to be indicating just that.

(2) what is the part # for the power supply to get a replacement part ?

(3) is it possible to use 3rd party (non-Apple) power supplies in the Mac ? If so, what would be the required specs ?

(4) any suggestions on where to purchase a replacement part ?


update: ended up replacing the power supply and the machine now starts up again. Both RAM boards have a red LED lighting constantly while the computer runs... is this normal or does this indicate another problem ? could not find anything regarding this in the service manual...

1 Answer 1


Having worked on Mac Pros of this vintage (the A1186 had 3 different models between Aug 06 & Mar 09) there could be any number of things wrong from a bad HD (the clicking) to a toasted power supply.

One nasty side effect of a zapped power supply is there is a possibly of some collateral damage to the main & peripheral boards, PCI cards, HD power supplies, etc, when it either degraded over time, experienced a sudden failure, or was electrically damaged by a bad AC power transient from the premises wiring.

You need to replace the PRAM battery as well. A simple alkaline CR2032 button battery should do the trick.

Removing and reseating every PCI board, ribbon cable, and RAM module is also recommended, but only if you know what you're doing! Replacement parts are next to impossible to find, however.

I assume you've followed the troubleshooting steps starting on page 152 of the MacPro A1186 late 2008 service manual (which I've included here for others who are seeking this info.)

Another option is something like this site for a source of spare parts, or just to start from scratch.

  • I'd change the battery & re-test before anything else. They can cause all kinds of random issues if they're dead.
    – Tetsujin
    Jun 26 at 7:27
  • thanks for the tip re the battery. just replaced that, same result. But, for whatever reason, one time while connecting the power cord (and the new battery in place). the white front LED now started blinking permanently... but no other time after that... HDD and everything else has been removed, PSU still makes the same two clicks... I guess I'll order a replacement power supply and see if that fixes it...
    – peterf
    Jun 27 at 5:22
  • updated the OP, finally replaced the power supply. systems starts up again but both RAM boards now have a red LED lighting constantly... is this normal ? Thx
    – peterf
    Jul 22 at 6:37
  • The red LED is most likely normal. If the System Report shows all installed RAM modules, then things seem to be working correctly. Congratulations! It is a wondrous thing when the POST startup chime fills the air, the screen flickers to life, and all is well.
    – IconDaemon
    Jul 23 at 16:49

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