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PowerMac G5 Dual 2GHz freezes any time, boots sometimes with one processor

Since two weeks I experience freezes at different up-and-runnng time. It could happen at grey startup screen (after a while fan goes wild), could be after some minutes working in a full booted user environment.

I run AHT several times, no error reported. When I took out all RAM except for Apple RAM, it still freezes at some time.

Now, by random, my machine starts sometime with only one processor and is stable for hours (only the fan runs higher and cpu load is most of the time near 100 percent). Activity shows one bar only, System Info says: Number of CPUs=1. I have no idea which processor runs and which "sleeps" deadly. iStat tells only about CPU A as having a temperature, the fans of CPU A run higher, but the fans of CPU B run also on a lower level.

The "U3 Heatsink" reads 65-70 degree Celsius. Is that (too) high?

Only once I got a kernel panic during verbose startup. It read:
"System failure: cpu=1; code =00000001 (corrupt stack)
unalined fram address: 0x00000001"

I am tempted to shut down one CPU with Open Firmware command, but will it be the defect one? At least the machine is doing something regular then, but is slow...

Any help is much welcome!
Yours, Whoopy

G5 dual 2GHz and G4 Titanium, Mac OS X (10.4.6)

Posted on Aug 20, 2008 4:59 AM

Reply
200 replies

Aug 20, 2008 6:55 PM in response to Whoopy

I am having the same problem and I did the same steps as you.

In addition, I ran memtest 5 times to determine if it was bad RAM. Everything checked out. I pulled out all of the peripherals except my Apple extended keyboard, Apple mouse and LG L246WP monitor. I'm still crashing.

I'm even crashing in safe mode!

I personally think it's a software conflict. I'm willing to bet I received a software update that was meant for an Intel mac. I'm about to purchase a new internal hard drive and re-install Tiger. If that doesn't work, I have no idea what it could be.

Aug 26, 2008 4:00 AM in response to Whoopy

After many reading in the forums and testing, installing, checking,
THIS is my working solution (compare "Technical Q&A QA1141" on Apple Developer Connection):

(boot Mac until Mac OS X is running)
1. Launch terminal application (found in folder utilities)
2. Check environment variables by entering: nvram boot-args
3. enter: sudo nvram boot-args="cpus=1" (add other variables given at step #2 in the quote)
4. Enter root or administrator password when prompted

(You can do the same thing with a slightly different comand when booting into Open Firmware)

I did that and since then my machine boots all the time, always running on one cpu (checked by Activity application and Mac Profile). Mac runs slower now but no crashes since then. Only problem still: if Mac goes to SLEEP it will freeze with black screen and the ventilator fans go to full speed. My workaround: Set preferences to "no sleep" and never force Mac to sleep manually.

When I get another system running I will try the processor re-seating and other measures.

SAD THING:
-no test (including Apple Hardware Test CD) showed any thing wrong with my cpus or RAM.
-many "tipps" cost hours of hours testing, installing etc. Installing a new system will cost many hours in running into application problems, re-installing drivers, fonts, etc.
-lastly: the problem occured a short while after my service contract was terminated...

Yours, Whoopy

Oct 13, 2008 8:54 PM in response to David Roland

I'm experiencing this too on a Dual 2.3Ghz G5.

The CHUD tools do not help, since once booted with one processor the system thinks only one is available to select. The NVRAM setting did'nt make any difference.

In my case I had a the fans go into overdrive while sleeping (locking the mac up), then the next restart failed with a no entry symbol. After repairing permisions & verifying disks, it boots, but with only one CPU.

Oh well, I guess it is 2 months out of Applecare now, what better time to halve it's power ?

Oct 14, 2008 8:34 AM in response to Samsara

Thanks for the links Samsara,

Weirdly leaving it without power connected overnight, but with the PRAM battery has reactivated the second processor. (My NVRAM boot-args are still set to cpus=2).

I'm not sure what to do other than hope it doesn't happen again? I have got the diagnostic CD from Apple (not the Apple hardware test, but the disc that does the thermal calibration etc) I think I'll run that to see if processor B reports errors, since last time I ran it it wasn't available to test!

Hopefully I won't need to replace the processor, I'm considering reseating it to be able to clear any dust that may be making it overheat.

Oct 14, 2008 1:31 PM in response to Drew Reece (Re:co)

Hi Drew,

While this is no light matter I just have to say I love stories where one walks away from their Macs with a problem only to come back and find it's resolved itself, at least for some amount of time. It's happened to me and I think thats one of the reasons why I'm prematurely bald and only half sane.

I wish you the greatest good fortune in your travails. These are really excellent machines. It's a shame they can be so unreliable. This being my third G5, as BC said, I feel your pain. Good luck.

Oct 14, 2008 6:58 PM in response to Samsara

I think I spoke too soon. It ran fine for hours. I shutdown (because I don't trust it to sleep at the moment) and restarted it a few hours later.

Only one processor showed up again.

I'm hoping tomorrow it will start up with 2 processors so I can quickly run the Diagnostic CD. The problem is that if the processor doesn't show up then the Diagnostic CD won't test it. It just stops existing and the system seems happy with that.

I'm wondering if the processor is dusty and overheating and somehow disabling itself once it has warmed up, I'd expect to be seeing kernel panics though. It makes little sense to me 🙂

A few similar posts have suggested reseating the processor as a solution. I may try it if I cannot get any help from my expired Applecare. It would allow me access to clean the heat sync I suppose.

Oct 17, 2008 12:46 AM in response to Whoopy

My PowerMac G5 Dual 2.0 also has this problem.
It all started one sad afternoon a month or so ago. I noticed that my computer was on and the fans were on full speed. As soon as I moved the mouse to shut it down, I got the wheel of death!
I had no choice but to do a force shutdown.
The next day, I turn my computer on and it just stayed on the gray screen with the dark gray apple, and no spinning thingy.
So once again, I had to force shutdown.
Pressing the 'Option' key did gave me the screen where one can select where to boot from; the main HD, booting CD, etc. but none of the worked.
When I chose to boot from my internal HD or from the restore CD it would just get stuck on the gray screen with the apple logo.
I pressed the PMU button = no change
I did a PRAM reset = it brought my G5 to life but then a few minutes later it froze and history repeated itself.
Did a PRAM reset again and this time didn't work.
Tried booting from my PowerBook G4 HD via firewire = frozen gray screen
When I pressed the 'T', i get the FireWire logo and I'm able to boot my G5's HD using my PowerBook G4. But when I put my G4 on firewire mode and try to boot my G5 by selecting the OS of the G4, I still get the frozen screen, so the problem is not with the HD.


One time I was able to boot my G5 from the 'Restoration CD' and I used the Utilities to Fix permisions, and repair the HD but still the computer would freeze and same old story.

Since I got this problem, It has work normal only 3 occasions but no longer than an hour until the fans go crazy and freezes.

I tried different memory sticks and no improvement.

My AppleCare expired on May, and my G5 went down 2 or 3 months after that.
This feels part of an strategy called "Get a(nother) Mac". Where comps are design to last just a little after AppleCare expires and then BOOM! no choice but to spend some serious cash on fixing it or use that money plus more to get one of the resent mac which have had some changes since one bought the mac that just went to apple heaven.

Anyways, I feel that the problem will be solved by replacing the two processors, heatsinks, or whatever they called it.

I took apart my G5 today and I'm not sure but it seems that the heatsinks might use some kind of gas to cools the CPUs or Chips and I think that gas is over.

Has anyone swap the heatsink units and noticed any difference?

Here's of the heatsink for the PPC G5 2.0
http://img186.imageshack.us/img186/2642/g5heatsinksw5.jpg

Oct 17, 2008 3:00 AM in response to Tenoch T

Tenoch T,

Your symptoms seem a little different to mine. My mac will boot and depending on how long ago it was last powered on this affects how many processors will work for me.

If it was on a few hours ago I get one processor, if it is left several hours I get 2 processors. It seems my problem is temperature related, possibly something is expanding with heat and loosing contact as the mac warms up. I haven't experienced as many 'will not boot' as you seems to have. I also only seem to loose a processor upon a restart, so perhaps it is something to do with the 'POST' tests that happen on startup.

The gas you refer to for cooling the heat sync is simply air, unless you have a liquid cooled system, but I don't think there were any 2.0 dual Ghz liquid cooled macs. The photo is for an air cooled heat sync.

I'd love to believe the conspiracy theories, but I think it would be very difficult for Apple to make a Mac that dies after the warranty, or Applecare runs out. It also would conflict with UK trading law and would bring a lot of people to take legal action against Apple.

If you allow the Mac to cool down (open a window) will it boot up? If it will install 'hardware monitor'- http://www.bresink.com/osx/HardwareMonitor.html to see what the temperatures are. You will need to watch them upto the point it shuts down. Let us know the results here.

Another thing to try is to clean out any dust inside the case. It is possibly to carefully suck it out with a hoover, but be very careful not to hit anything inside the case.

There is a 'Service Source' manual that is for Apple technicians available if you do enough googling. It can help you diagnose the fault, but you need to be technically competent before you do any of the surgery to your mac.

Oct 17, 2008 8:49 AM in response to Drew Reece (Re:co)

Hello Drew!
Thank you for responding. The 3rd time that my G5 booted up fine was 3 days ago. Previous to that I had not touch it for about 2 or 3 weeks, so I guess that's more than enough time to cool down. But now, I have booted it after 24hrs since I last try and still it gets stuck on the first booting screen. What's interesting too is that if I try rebooting several times, it gives me a black screen instead, no booting screen at all. This is when I leave it alone and don't come back to it until a few days later.

About the cooling , to be honest I'm not sure what my G5 uses. But it seems that my model doesn't use a liquid cooling system.

I have clean my G5 using a soft brush and dust remover air cans, I saw some photos of a very dirty power supply, the PS is the only thing I haven't clean.

About the 'conspiracy', I hope is not true either. When I google my problems of my G5 freezing on the booting screen, I've notice that most of the computers that have this similar problem are from computers sold early or late 2005 and the problems seem to be poping out after 3 years which oddly enough is when applecare expires.

Thank you for the link, I'll install 'Hardware Monitor' as soon as my G5 boots and I'll post here how everything goes.

Oct 17, 2008 12:46 PM in response to Tenoch T

I'm sure you have tried this, but I think suggesting it would be worth it.

Hold the mouse button down on startup (to eject the CD/DVD tray) insert your Mac OS DVD and boot from that. There should be instructions for using the Apple Hardware Test on the original mac CD/ DVD. I think its by holding alt @ startup, then selecting the AHT volume. Run the tests & Google/ search Apple.com for any errors it reports.

The 'Service Source' manual is invaluable for tracking down faults, but I don't think it is meant to be distributed to non-Apple approved tech support, so you will need to find that on your own. Just use google & the model in your queries, eventually you'll find a fantastic PDF.

There is an alternative guide here (probably for a different model).
http://www.sharpeningbeneath.com/g5guide/

One thing I have seen inside the case is a lot of dust/ dirt in the power supply unit (PSU). The PSU in the G5 is right at the bottom of the case, so if the mac is on a floor, it ***** up all the dust at floor level. Use a hoover outside the case and then try using the air duster to loosen any dust, and direct it towards the hoover nozzle. Do this at the front and back of the case. Sadly the only effective way to clean it is by stripping the unit.

I'm off to the local Apple Store to see if what can be done (if anything). A few people have suggested calling Applecare, and being polite can sometimes get it fixed/ checked for free when the warranty has expired recently. Applecare should also tell you if the unit has been recalled, but you may have not seen the recall announcement.

Good luck,
Drew

PowerMac G5 Dual 2GHz freezes any time, boots sometimes with one processor

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