On button power failure -- causes intermittent start

Hi,
I generally don't leave use many USB/Firewire devices connected. But two of my rear USB connectors are used for two Eizo screens which are used as a hub for a few devices (USB headset, Griffin Powermate, Wacom, iPhone dock) so the power comes from the screens I think. Otherwise the last one is for my keyboard. I leave the two front connectors empty or for occasional use. Nothing has change since one year in my set-up so... Bye!

There have been some anecdotes that overdrawing the total budget for power for the rear USB ports (1500 milliamps) or the front USB ports (1000 milliamps) can cause a click and sudden poweroff.

Electronic components may drift with time, and corrosion can change the resistance slightly over time. You may be near overload, but only cross the line from time to time.

You could try moving USB stuff around so that the load would be lower on each group (front and rear) or move more stuff to the powered Hubs in displays and other devices.

Hi,

I don't understand. Why I would have suddenly too much load on my two rear USB ports as they are connected to two individual Eizo screens... they should use the help of the power of each screens. Isn't that right ?

Bye

+(I doubt I can bring this Mac Pro to repair before Christmas... I keep restarting once or twice a day till I finished important things to do)+

I'm not jumping on this thread but I do have exactly the same problem with my early '98, quad-core xeon mac pro and this info might be useful.

It's only just surfaced after I had a 'blue screen' on start up issue, which was solved with a 'safe mode' start up. But now I get a power cut with a restart about 10 minutes after I get going in the morning. Sometimes it repeats, often it will settle down and work fine for a hours. But this morning when I restarted in 'safe mode' one of the fans went into overdrive and was making a huge din.

I've unplugged all usb's apart from the printer and keyboard/mouse. I'll follow this thread with interest and also post this on a new thread.

I have the same problem with my MAC PRO 2008.

It shuts down by itself after one-week normal function.

When trying to turn on, there comes a clicking sound and it doesn't turn on.

After removing power cable for hours, it starts normally.

Anyone found a solution?

Message was edited by: sajw1971

Hello,

I am experiencing the exact same issue as waltmorton. The symptoms are just as he described them: 2008 Mac Pro, solid performance, within the last two months I go to power it on and get a "click" - a pause of about 3 seconds - and then another "click", with no other reaction whatsoever. With plugging and unplugging the computer powers on 20% of time or so. It's invariably all or nothing. Once powered on the computer runs as normal.

The very first time this occurred was a case where I went to wake the computer from (a long) sleep and it was unresponsive. I had to do a hard shutdown. For now I have disabled sleep modes as this problem continues.

So far I have
-reset PRAM
-reset SMC
-performed system reinstall
-cleaned the interior of the system

The problem hasn't changed.
the only anomaly I've noticed was after cleaning the system, one DIMM of RAM (of two) was no longer showing up. After reinstalling it reappeared.

All I can say definitively is this is not a Snow Leopard issue, as I am still on OSX 10.5.8

If I can find window to take to a technician I will, but I'm curious if anyone here has any new leads or suggestions, I'm all ears.

Hi,
Thanks for posting, looks very similar...
The problem started getting worse a little for me since. Now I have a doubt about the power supply issue. I think it's more likely related to an eletronic resistance, heat or other sensor that interfere when using high calculations... just guessing because it shut down abruptly more often when I attempt to render a complicated scene with after effect using more heavy multiprocessing (To me it's definitively a hardware, not a software or system issue). Anyway, I'll share my feedback later, I'll definitively bring this machine to repair within the next 7 days...
Best wishes anyway !

all of first I gotta apologized for my bad english, anyway, i have the same problem as u guys got, and lucky me my mac pro still under applecare, so when it happens like a month ago, i gave a call to apple, and ppl said it might cause my power supply, and they got a new one and replaced it, it runs fine.......for "a week" then it back to the same problem, then i called to apple care again, this time they said it should be the motherboard problem, and they got a new one and replaced it, well.... it works fine..... for "a week" again, and back to same issue...... well..... i give them a call tonite...... or i should give an email to steve jobs?

Just in case, here is the "noise" my MacPro do when it suddenly shut down/restart ... (looks like the hard drive head moving or from the DVD drive ??

http://snd.sc/eZ2lIN

Yeah, that click sounds very familiar. Someone suggested it sounds like a faulty relay?

Just to confirm my early '08 mac pro (not '98??) has gone the same way. Nothing has changed in my set up recently but now it switches off intermittently and tries to restart. Eventually the fan goes into overdrive and I'm left with a black screen.

I've done an SMC reset but no joy. Anyone know what is going on with this? I can't find any earlier discussion of problems like this and it seems odd that we've all suddenly developed this issue.

I've also noticed that when my machine tries to restart (and fails) I can hear a revving noise, like the fan is trying to start up but can't.

Last one (I'm in get task done mode) - is it possible this could be either a fan problem or failure caused by a dust build up? My machine is fairly dusty and I found one old thread that suggested this could cause problems.

Definitely the last one - here's a link to the archived thread that suggested dust build up might be the problem. http://tiny.cc/c7yua Some people found this worked; some didn't.

It seems there are a number of different symptoms being discussed here that may or may not be from the same root problem. In my case, the computer has never actually shut itself off when running - the only symptom is that a large majority of the time it simply won't power on at all. This behavior seems in line with waltmorton's original post.

That being said, I am doubtful that my problem stems from dust buildup and I am certain that it is not a USB issue. The very first thing I did upon experiencing this issue was to clean the inside of my machine. I tried to do a thorough job, removing the fans w/ casing and cleaning all components. Yet the problem persists. Also, my machine has the 8800 GT, not the ATI model that was referenced as having the major buildup. As for USB, I have a wireless mouse and keyboard, and unplugging all peripherals from the machine did not have any bearing on the startup problem for me.

I can't come up with any specific change I've made to the system that would result in this problem, which leads me to believe it is an internal hardware issue, probably a damaged or worn power component - people have been suggesting a faulty relay....?