Mac Pro 2008 Intermittent Power Problem

I bought a dirt-cheap second-hand Mac Pro 2008 which I knew hand a slight power issue, in that it would sometimes switch itself off and sometimes not power up for a while (although both these issues were separate).
This was what I was told, however, in practice it hardly faulted at all. That is, until I decided to update the OS.
I'm hoping the symptoms I describe will be useful to one of you hardware gurus out there and help me fix the problem.
The machine came with 10.5.8. I went through the update processes required to take it to El Capitan, and it would switch off every time during boot.
I then went back to square one and decided to do things in stages. At 10.6.6 the machine would boot up and work for a while, from maybe 30 minutes to a couple of hours, then power off.

It worked long enough for me to up it to Yosemite, where I get from 20 seconds to a couple of minutes use.

So, it seems that, as I move further up the OS's, it wants to power off more readily.

I'm no techie but I'm guessing that perhaps each OS inherently draws more power and thus creates the problem more quickly.

Hoping it's a component I can easily replace

TIA

geordienz said:

I then went back to square one and decided to do things in stages. At 10.6.6 the machine would boot up and work for a while, from maybe 30 minutes to a couple of hours, then power off.

It worked long enough for me to up it to Yosemite, where I get from 20 seconds to a couple of minutes use.

So, it seems that, as I move further up the OS's, it wants to power off more readily.

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Firstly welcome to Mac-Forums.

Second. Can you tell us the exact model of the 2008 Mac Pro? There were a couple different models in 2008…and it can make a big difference with what you are doing.

Third. I don't think that the problem has anything to do with the OS version that's installed. Sounds more to me to be either a temperature issue or a power supply issue. Of course if the problem does seem to get worse with newer OS versions…there could be a relationship…in that a newer OS may "push" the computer to work a bit more…increasing the temps…or more of a burden on an older-weaker power supply.

But the basic problem is hardware based (cooling system funky or dirty)…or a weak power supply. Since other Mac Pro's of the same vintage don't have a problem.

- Nick

p.s. Also. Do you know if the CPU's in this Mac Pro have been upgraded?

pigoo3 said:

Firstly welcome to Mac-Forums.

Second. Can you tell us the exact model of the 2008 Mac Pro? There were a couple different models in 2008…and it can make a big difference with what you are doing.

Third. I don't think that the problem has anything to do with the OS version that's installed. Sounds more to me to be either a temperature issue or a power supply issue. Of course if the problem does seem to get worse with newer OS versions…there could be a relationship…in that a newer OS may "push" the computer to work a bit more…increasing the temps…or more of a burden on an older-weaker power supply.

But the basic problem is hardware based (cooling system funky or dirty)…or a weak power supply. Since other Mac Pro's of the same vintage don't have a problem.

- Nick

p.s. Also. Do you know if the CPU's in this Mac Pro have been upgraded?

Click to expand...

Thanks so much for the prompt response, and for the welcome.

It's an early 2008 3,1.
I don't think the CPU's have been upgraded but I can't even check at the moment since it only powers on for about 2 seconds now before cutting out

geordienz said:

It's an early 2008 3,1.
I don't think the CPU's have been upgraded but I can't even check at the moment since it only powers on for about 2 seconds now before cutting out

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Good deal that it's a Mac Pro 3,1. Earlier Mac Pro's (1,1 and 2,1) had a max OS of 10.7.5…and to go higher…a person needed to do some "special stuff" to get newer OS's to run. Mac Pro 3,1's and newer can officially run the latest Mac OS.

Sorry to hear about the short "on time". I'm wondering if you were able to get back to the state it was in when you first got it (OS 10.5.8)…you would have longer run-time before shutting down (which you said it was fairly stable then…or at least more stable).

I still think that the problem is hardware related. If the computer is completely cool (not run for a while)…and if it's still shutting off after only a couple seconds…then that could point more & more to a power supply issue.

Any way to get 10.5.8 installed again? Or maybe what I should ask is…what happens if you try to boot it from a 10.5 or 10.6 install DVD?

- Nick

pigoo3 said:

Good deal that it's a Mac Pro 3,1. Earlier Mac Pro's (1,1 and 2,1) had a max OS of 10.7.5…and to go higher…a person needed to do some "special stuff" to get newer OS's to run. Mac Pro 3,1's and newer can officially run the latest Mac OS.

Sorry to hear about the short "on time". I'm wondering if you were able to get back to the state it was in when you first got it (OS 10.5.8)…you would have longer run-time before shutting down (which you said it was fairly stable then…or at least more stable).

I still think that the problem is hardware related. If the computer is completely cool (not run for a while)…and if it's still shutting off after only a couple seconds…then that could point more & more to a power supply issue.

Any way to get 10.5.8 installed again? Or maybe what I should ask is…what happens if you try to boot it from a 10.5 or 10.6 install DVD?

- Nick

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I think I could get it to 10.5.8 if I could get it to power up.
At this time it's not even getting power to the main fan. Fan on graphics card powers up for about a second then cuts.

geordienz said:

I think I could get it to 10.5.8 if I could get it to power up.
At this time it's not even getting power to the main fan. Fan on graphics card powers up for about a second then cuts.

Click to expand...

Again…if it was working somewhat previously. Then this kind of points to a worn out power supply. This is especially true if the computer had a lot of "on time" hours before you got it. And if those "on time" hours were busy doing heavy duty rendering (all the cores being used).

- Nick

pigoo3 said:

Again…if it was working somewhat previously. Then this kind of points to a worn out power supply. This is especially true if the computer had a lot of "on time" hours before you got it. And if those "on time" hours were busy doing heavy duty rendering (all the cores being used).

- Nick

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Thanks Nick.
I know it was being used for heavy duty video work. PS easily replaced?

geordienz said:

PS easily replaced?

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Personally I don't think so (doing stuff on laptops is more complicated & delicate). But according to ifixit.com…they rate it as a "Difficult" repair:

https://www.ifixit.com/Guide/Mac+Pro+First+Generation+Power+Supply+Unit+Replacement/32222

- Nick

pigoo3 said:

Personally I don't think so (doing stuff on laptops is more complicated & delicate). But according to ifixit.com…they rate it as a "Difficult" repair:

https://www.ifixit.com/Guide/Mac+Pro+First+Generation+Power+Supply+Unit+Replacement/32222

- Nick

Click to expand...

Looks simple enough - thanks!

geordienz said:

Looks simple enough - thanks!

Click to expand...

Great you think so too!

A Mac Pro 3,1 is still a good computer (IMO)…and worth investing in a replacement power supply.

Good luck with the repair. Try to get the replacement PW from a place you can return it to (just in case its not the PW).

Please let us know how things go.

- Nick

Yeehaaar!!

pigoo3 said:

Great you think so too!

A Mac Pro 3,1 is still a good computer (IMO)…and worth investing in a replacement power supply.

Good luck with the repair. Try to get the replacement PW from a place you can return it to (just in case its not the PW).

Please let us know how things go.

- Nick

Click to expand...

Being in NZ, beggars can't be choosers when it comes to a lot of Mac/PC spares, so I took a chance and ordered a PS from China (not even knowing if it was, for certain, a PS problem).
The 'difficult' fix proved to be a piece of cake and I'm glad to say my Pro is running like a dream . . . so far

Thanks so much for your help.

geordienz said:

Being in NZ, beggars can't be choosers when it comes to a lot of Mac/PC spares, so I took a chance and ordered a PS from China (not even knowing if it was, for certain, a PS problem).
The 'difficult' fix proved to be a piece of cake and I'm glad to say my Pro is running like a dream . . . so far

Click to expand...

That's GREAT to hear…glad things are working out so far!!!

Yes. When we repair our own computers like this…there always is a bit of uncertainty if we've identified the correct "bad" part. We troubleshoot throughly…and try to logically narrow things down to the most likely issue…then replace it. Great job!

- Nick

p.s. Didn't know you were in NZ. Maybe add your location to your Mac-Forums profile in case it comes in handy in future discussions. I think that we have at least a few members from NZ.