Mac Pro Tower wont turn on. How to trouble shoot power supply

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blackwell99 Author

Level 1

4 points

Mac Pro Tower wont turn on. How to trouble shoot power supply

Hi all,

I have a early 2008 Mac Pro Tower.

I shut it down during a storm because of power glitches, the next day it would not start.

Pressing the Diag Switch on the Main Board give a yellow led, showing stand by power is there.

Holding the Start Button down and pressing the Diag Switch gives no lights.

Pressing the switch right below the Diag Switch give 2 red leds when the switch is released.

Am I correct that the lower switch resets the SMU?

I'm assuming at this point that it is the power button, but if I test the power button and find that it's working,

whats the best way to trouble shoot the power supply?

Thanks

Mike

Mac Pro, Mac OS X (10.6.8)

Posted on Oct 27, 2015 8:28 AM

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Answer 1

Oct 27, 2015 9:11 AM in response to blackwell99

You can download the Service Manual for your Mac here. The diagnostic section is pretty complete. Exactly what happens when you press the power button as you normally would? Are there any other sounds beyond the first click?

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Answer 2

blackwell99 Author

Level 1

4 points

Oct 27, 2015 9:19 AM in response to FatMac-MacPro

Thanks 🙂

It doesn't even click. Nothing happens at all.

Thats why I was thinking the start button is bad.

Mike

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Answer 3

Oct 27, 2015 9:29 AM in response to blackwell99

I asked because something similar happened with my 2010 Mac Pro. The culprit turned out to be an almost dead CMOS battery but the power supply was a bit shaky too. Unfortunately, the diagnostic section for that Mac Pro isn't nearly as complete as for yours.

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Answer 4

Oct 27, 2015 9:44 AM in response to blackwell99

When a "mature" Mac will not start after being off AC power, the first thing (and the easiest thing) to check is the 3 Volt coin cell battery that backs up the PRAM.

That battery is half-hidden behind the graphic card. Its holder is 'delicate' -- do not force it or it will break. Testing it in circuit is complex -- if AC power plug is in the socket, you will measure the "always-on" power supply rather than the battery.

Replacing the battery means your Mac can now remember -- but what it remembers is still garbage until you do a PRAM Reset.

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Answer 5

blackwell99 Author

Level 1

4 points

Oct 27, 2015 9:42 AM in response to FatMac-MacPro

Hi,

I replaced the battery a couple of years ago. It would start up but had other problems.

But thanks for the manual link. I just have to bite the bullet and tear it down so I test the power button.

Of course the manual says it can be the front panel board too.. Fun and games.

thanks

Mike

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Answer 6

blackwell99 Author

Level 1

4 points

Oct 27, 2015 9:56 AM in response to Grant Bennet-Alder

Hi,

I replaced the battery a couple of years ago. But that was one of the first things I checked,

it has 3.17 volts so it should be fine.

Thanks

Mike

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Answer 7

Oct 27, 2015 10:08 AM in response to blackwell99

3.17 volts so it should be fine.

Agreed.

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Answer 8

QkaG

Level 1

8 points

Oct 27, 2015 6:18 PM in response to blackwell99

Does your small white power light above the on button at flash on, then off? My 2008 tower also would not start. It turned out to be a bad memory module.

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