Mac Pro 3,1 (early 2008) Power/Boot Issues (Long post!)

[bloomfeld]

In the last days, I experienced the same symptoms the OP has mentioned before. My 3.1 switched off a few seconds after booting, sometimes with a kernel panic, but most times without. Just like a power outage. Some months ago only half of the RAM was recognized, but this was fixed with simple reseating. I thought it would be the PSU, which would have meant EOL for my Mac, because I'd had to pay 300 Euros for a new one.

But behold: it turned out that the power-outs stopped after I took out half of the RAM! Riser card B showed a red LED on DIMM2, so I feared the riser card would be the culprit. But then I examined the riser card slot and found a huge clog of dust in front of it. In fact, part of it had been pushed into the slot when reseating the RAM! So I disassembled the processor and end fans and cleaned the parts as much as I could. Boy, what a mess! The dust has been literally compressed inside the RAM slot!

After reseating, everything seems to be normal again. So I may have been lucky without a short circuit on the riser card. Hope I'll get some more years out of my 3,1 as this machine was the best buy ever.

However, I'll keep in touch and will report how it works in the next weeks.

TL;DR: Mac Pro switches off in a power failure fashion. It turned out the PSU wasn't the culprit, but a dust clogged RAM slot. So keep your Mac tidy

 

[TonyK]

Well our issue in my wife's 4,1 was a dead PSU. Had it replaced and it is working fine. Only issue was the shop didn't seat the super-drive assembly in fully and the drive would not open. I re-seated it quickly but will power down this weekend and take it out and re-seat it.

 

[Sculptor57]

Hi everyone,

Posting today after a long road of trial and error. I finally parted with the cash for a new motherboard. I had inexplicable crashes with no core dumps. Neither I or the Mac Shop in town could pin it down. The Mac Shop WAS able to confirm that Yosemite and Flash will not play on this tower at all.
Upgrading to El Cap. fixed the problem.
A short in the board itself was diagnosed and a tested board was installed as replacement. I have been running using the OS screensaver and normal power save options. I have run normal operations with occasional Photoshop. I have not tried any heavy CAD use yet.
I have sometimes shut the Mac down for a few days, and sometimes left it running for a few days. No change. It's been about 3 weeks and no crashes.
After all the reading I have done here, I hope my experience helps someone else.

 

[bloomfeld]

TL;DR: Mac Pro switches off in a power failure fashion. It turned out the PSU wasn't the culprit, but a dust clogged RAM slot. So keep your Mac tidy

Just a heads-up on this: The switchoffs continued to happen a few days after posting this. So I replaced half of the RAM with fresh modules. No more switchoffs since then!

So I guess it's safe to say that RAM failure was the culprit of the switchoffs.

 

[MrAverigeUser]

Just a heads-up on this: The switchoffs continued to happen a few days after posting this. So I replaced half of the RAM with fresh modules. No more switchoffs since then!

So I guess it's safe to say that RAM failure was the culprit of the switchoffs.

I experienced same problm with a MBP 2 years ago.

Random kernel panics and shut downs, etc.
The auto- diagnosis showed everytme "test passed"

So I thought more abput having a problem with my SSD or perhaps malware on the disk.
Went to a very reputated apple-accreditated service and they found out that one RAM unit was failing although the initial "diagnostic test" every Mac does afzer starting showed alwaS "ok" !
After exchange of the RAM everything was pretty nice as before!

So - always think also about failing RAM !
Especially since running a test with other RAM is that simple!


As for failing PSU:

Somewhere her in the MR forum I found a good posting about the PSU from someone living in HongKong.

He explained that the capacitators are the prpblem. Life expectation of PSU is only limited by these capacitators which tend to reach their life expectations after about 4-5 years. There is a wide range of quality concerning capacitators. The only thing you have to domis exchanging capacitators - but you have to be shure that you choose the good ones.