G5 Quad CPU B heat issues

Hello,

I have a Powermac G5 Quad late 2005 model. For the last couple of weeks I have noticed that the fans are blowing more than usual when the computer gets busy. I opened the door to check if there is coolant leakage or dust. I cleaned some dust, but cannot see any loss of coolant. The system still makes the somewhat high pitch tone, so I assume the waterpumps are working. Also Apple Service Diagnostic 2.6.3 does not show any problems, although it won't calibrate the temperature sensors.

I used Temperature Monitor, which shows that CPU B runs at about 45 C degrees, while CPU A is about 33 C degrees, when no applications are open. When I start using some apps, CPU B spikes to about 60 C degrees, the fans start blowing, and it settles down at about 50 C degrees with the fans still blowing.

The machine has been in use pretty much and I'm aware it's out of warranty, but I wonder what could be wrong with it and if it can be reasonably repaired. Perhaps this is common wear and tear, considering the liquid cooling, but I certainly did not buy that machine to trash it 5 years later. When I buy anything new I would like to use the G5 for some back-end tasks.

What can I do?

Thanks for any advice.

Posted on May 8, 2011 7:21 AM

29 replies

May 11, 2011 1:02 PM in response to Markus Waldorf

I carefully cleaned the complete system with a compressor, removed the old thermo paste from the CPU's and reapplied new one (Noctua NT-H1). After I reassembled the system I was very happy to notice that it started up right away without showing any trouble.

The readings in iStat Pro have changed. Without doing anything, CPU A now runs at 30 C degrees, which is 10 less than before, but CPU B shows 70 C degrees, 20 more than before. The bottom pump and hoses are almost hot, but the upper pump and hoses seem room temp. I don't think a 40 C degrees difference between the CPU's is normal. I suspect that there is no circulation going through the lower pump which is why it is hot. iStat Pro shows the same 3600 rpm for both pumps. The fans were blowing around 3700 rpm. There is also a new rattling noise coming form the pumps.

After a normal shutdown, the system won't startup again showing a red overtemp and quickstop LED. Leaving the system rest for 10 min. made no difference.

I guess that's it then.

May 11, 2011 1:57 PM in response to Markus Waldorf

I let the system cool down for 1 hour and it restarted, with the overheat LED on. CPU A is at 30 C degrees, but CPU B shows 86 C degrees now. Could this be the result of reassembling or is this rather a hardware issue with the LCS systems that may have manifest now since the system was not in use for a couple of days?

japamac

Level 7

24,400 points

May 11, 2011 4:15 PM in response to Markus Waldorf

Could this be the result of reassembling

When in doubt, I always take it apart and do it again.

is this rather a hardware issue with the LCS systems that may have manifest now since the system was not in use for a couple of days?

It could be that the failure was imminent and this is coincidental.

Either way, the machine can't run as is.

May 11, 2011 7:03 PM in response to japamac

I did the same procedure again, and this time I even switched the processors around. Same result, CPU A 30 C, CPU B 85 Celsius. So the LCS is trashed.

japamac

Level 7

24,400 points

May 12, 2011 1:36 AM in response to Markus Waldorf

Same result, CPU A 30 C, CPU B 85 Celsius. So the LCS is trashed.

Agreed.

May 12, 2011 2:15 PM in response to japamac

I wonder if the system would work if I remove CPU B completely. Has anyone tried that?

BDAqua

Level 10

250,259 points

May 12, 2011 2:47 PM in response to Markus Waldorf

The cpus boot argument can range from 1 up to the total number of processor cores on your system.

http://developer.apple.com/mac/library/qa/qa2001/qa1141.html

You might try this also, thanks to old comm guy...

This can be done in open firmware,(boot with cmd+option+O+F held down).

setenv boot-args cpus=1

reset-all

Since the Quad has 4 cores, you might try cpus=2

romko23

Level 2

408 points

May 13, 2011 9:26 AM in response to BDAqua

Ok BdAqua.. now you have me worried. I just got off the phone with my friend who works at AMA Systems in Columbia, MD - he told me as far as he knows by reading the Late 2005 Service Manual there is no mention of re-applying heatsink paste to the processors, and would require a new LCS with processors. Is he right? He told me he doesn't want to take the chance and pull off the processors as they are attached to the LCS. Also, he told me that part of the processors are attached on the bottom of the logic board as well.

Also, can you show me a pic of gumming on the LCS? I hope I am not suffering from this also.. I am somewhat concerned, though my temps don't go very high even under full load.

Areas where I have noticed an increase in fan speed are: When the G5 goes into screen saver mode - running flury screen saver or other screen saver. When using a data recovery software.. and while my AHT and ASD report no problems at all, there is no software out there to control the G5's fans? I am surprised that smcfan control won't work as the G5's like the mac pro have SMC and not PMU.

BDAqua

Level 10

250,259 points

May 13, 2011 11:31 AM in response to romko23

Sorry, I can't answer that, but might see the last post here...

http://forums.macrumors.com/archive/index.php/t-1099519.html

romko23

Level 2

408 points

May 13, 2011 2:49 PM in response to BDAqua

Ok, sounds like I am just going to leave it alone.. Its not a problem at all, as my temps are well within range.. I guess screen savers and processor based programs cause the fans to rev up. I have my processor settings on HIGHEST, so I will just go back to AUTOMATIC. I don't use REDUCED as I need the full performance of the Quad for most of the stuff I do.

I am just going to go by what Apple told me in terms of having to maintain the LCS; they told me since its a sealed system, I wouldn't have to bother doing anything.

May 13, 2011 5:14 PM in response to Markus Waldorf

Many thanks to everyone. I think I have found a temporary solution. Below is a summary. Someone will hopefully find it helpful.

SUMMARY:

Hardware:

Powermac G5 Quad. LCS is labeled Cooligy with 2 black pumpsfrom Delphi. CPU unit is processor type 2 as shown in the Apple Service manual.

Symptoms:

The fan activity of the computer started to become very annoying for no reasons. The iStat Pro widget reported 30 degrees Celsius for CPU A and 45 C for CPU B when the system was "idle". Under light usage there was a thermal disparity of 45 C for A and 60 C for B. Temperature would reduce to 50 C, but causing persistent fan activity of over 2500 rpm and pumps running at 2700 rpm, making the system unusable.

Troubleshooting:

I removed the CPU unit from the box according to the Apple Service manual. I cleaned the system with compressed air, removed the 2 CPU boards and renewed the CPU thermo paste. There were no signs of any coolant leakage or corrosion. The system looked spot on.

I used Noctua NT-H1 thermo paste. You only need to apply the size of a small corn seed. Due to how the CPU and heat transfer module are mounted, it will displace pretty much all of it.

After reassembling the system it started up fine, but CPU B would very soon overheat, causing the red Overtemp and Quickstop LED to go on. It got worse after a couple of system restarts, up to the point where the system would not startup anymore. Overtemp and Quickstop turned on right after power on, even when the system was off for an hour. Switching the cpu's around did not affect the problem.

Problem:

The CPU's are fine, but the liquid cooling system is failing due to some internal defect. Removing the unit and operating it after a longer break or in a different position seemed to have made the problem more apparent.The hoses of CPU B are warm; the ones for CPU A are not. There is obviously nocoolant circulation for unit B, causing it to overheat very quickly.

Conclusion:

I removed CPU B from the system by removing the complete CPU board from the cooling unit. The system now identifies as Dual Core G5 2.5 GHz. Thermal calibration from the Apple Service Diagnostic CD 2.6.3 ran successfully, unlike with both CPU boards installed. CPU A reports 40 C when idle, and up to 55 under high workload. The fan activity seems normal again. I can remove the CPU unit blindfold now.

CPU B is located at the bottom, close to the absorbent pad and power supply. The system will not startup with CPU A removed. Without CPU B, the system will run fine, but the red CPU insert LED will be on permanently. I had to reset the PRAM to get mouse support after starting from the Apple Service Diagnostic CD.

Comments:

There are reports about LCS repair and coolant refills available on the web. These systems suffered coolant leakage. The LCS in the G5 Quad is improved. It's a sealed system and certainly not to be maintained.There is no maintenance information available about how to refill the coolant properly, which could result in coolant leakage. The coolant liquid is very toxic and takes special handling.

There is probably not enough room in the box for conventional air-cooling of 2 processors under reasonable fan activity.

The Powermac G5 Quad is a masterpiece, if only it would last longer or could be maintained. The vendor, not Apple, told me that 5 -7 years is an average lifetime for a G5 Quad. I think it is unusual that a computer requires a repair that is more expensive than a complete new system after 5 years. It was not a $ 50 item. Unfortunately there is no reasonable Apple contact were I live.

At least I got the system working again, without 2 processors though. Only time will tell how long the cooling system will last until it breaks down completely. I currently need a system with a SCSI adapter and would rather buy an iMac than Mac Pro in the future. I'm disappointed that Apple does not offer a special G5 Quad repair policy.

Thanks.

romko23

Level 2

408 points

May 13, 2011 5:31 PM in response to Markus Waldorf

I too firmly believe the G5 Quad is a masterpiece and a wonderful system. But why would my friend, who is an Apple Authorized Service repair person, not take apart my Quad to re-apply heatsink paste, and then he told me that it is not needed.. otherwise, he would have to replace the whole unit. The Service guide doesn't say if heatsink paste should be replaced or not though..

But, even under no load or light load, the fans do come on.. I can see the LCS is working though as no CPU overtemp lights are coming on at all. So, is it just best to leave it alone as it is, or can the processors' paste be changed without disturbing the LCS?

The person whom I bought the Quad from told me he has never had any problems at all with it and rightfully so. The only thing he changed or had repaired was during the time there was a power supply recall and the machine's serial number fell in line with the power supply replacement program. As far as the vendor who told you this, thats up to speculation and depends on a great many things from ambient room temperature to maintenance and power cycling. I must have power cycled my Quad more than 20 times and the LCS(revision 2 which is the better one by Cooligy) just keeps chugging right along with no problems..

And the LCS is a sealed system, not to be opened by anyone other than Apple. I am familar with the original one the Quad came in and have seen the amount of leaks that one reported, but according to that site I sent to BDAqua, the LCS leak rate for the Quad is less than 1 percent.. not bad for a G5.

May 14, 2011 1:03 AM in response to romko23

Replacing the thermo paste is not going to be useful, but should be done when you remove the CPU from the cooling module. The cooling system looks like it is not designed to be maintainable by anyone and it is necessary to replace the whole enchilada when it fails. It's a real pity that the hardware will expire soon after just a few years and repairing it is not an economic solution because it was probably not considered. Trashing the system due to a cooling defect is also not economic.

romko23

Level 2

408 points

May 14, 2011 1:22 PM in response to Markus Waldorf

Well, if the original owner bought this in 2006 which he did, that would make it now close to 5 years old.. I just ran Thermal Calibration and all tests passed, no problems. As for a backup, I do have a backup LCS revision 2 that I got for like 150.00 off ebay with the processors in tact. The guy told me the whole thing is in excellent working condition, just that he parted out the G5 because of a case defect or something along those lines, so price is no object here.. Just that I'd like to replace the heatsink paste, but my friend at AMA Systems - Apple repair center advises me that the service manual does not call for replacing the thermal paste.. I tend to disagree though, but he won't touch it.

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G5 Quad CPU B heat issues