G5 fan problem after cooler disassembly.

[DeviousDan]

Hi All,

Got a dual 2.5Ghz G5 (PPC) here that runs as our server.

I got here (work) after the weekend to find it howling away and unresponsive. After investigation i discovered the system was overheating as the coolant from the water cooling system had been slowly leaking. Anyways i took it to a apple service centre and they quoted me $1700 to replace the cooling unit (haha), and they told me they could not be repaired.

I chose not to listen to them and disassembled the unit myself and repaired it with about $50 worth of equipment (but that's another story...)

Anyways after reassembling and starting up the fans have always run full blast. You might instantly think "That's because you didn't fix the cooling problem, they're still overheating!".. you'd be wrong. Temperature on CPU dies is 36c idle, can get to 50c under load. These temps are not high.

Now I've tried resetting the PRAM, changing the energy settings to "reduced" performance and tried resetting the PMU.

I've also tried to boot into open firmware with cmd + alt + O + F, but this does not work, the screen stays blank and the computer requires a reboot. I'f i could boot to OF then i may be able to reset NVRAM but who knows if that would help.

I can only think that removing the CPU's makes the mac think that the CPU's may have been replaced and as it doesn't know the specs of the possibly new CPU's it just overcompensates with cooling.

I'm at a loss here for things to try, the G5 functions beautifully apart from the fact it sounds like a jet engine. I would really appreciate some help before i go crazy from the noise....

 

[chscag]

I don't know if the G5 has thermal sensors similar to the iMac or even MB and MBP series, but if it has, that's where I would look. There have been cases of fans running wild or at very high RPM which were the result of a defective or accidentally disconnected thermal sensor.

As a start, go back over the work you did to repair the coolant system and see if all the thermal sensors are connected properly. You should be able to get an idea of where they're located by consulting the take apart instructions for your model G5 at:

iFixit: Apple Mac, MacBook, iPod, and iPhone Repair Parts

Also, I'm assuming you applied thermal paste (heat sink compound) when you assembled the cooling system back to the CPU.

Regards.

 

[DeviousDan]

Just incase this helps anyone in future...

I solved this problem by acquiring a "Apple Service Diagnostic" Disk. Apparently you can find images of these disks on torrent sites...

Once i'd booted to the disk i just ran the "Thermal Calibration", rebooted and now i have beautiful sweet sweet silence!

 

[chscag]

Thanks for posting back. But I'm curious about how the "Thermal Calibration" software works? Any idea? I wonder if it has anything to do with adjusting the thermal sensors"?

Anyway, glad you got it running. Have fun.

Regards.

 

[DeviousDan]

I assume the calibration puts the CPU's under load with the fans at a constant rate to gauge the efficiency of the cooling system. Then it adjusts the fan speeds for idle and load as required to stay under the maximum operating temp (which seems to be 88c). The fan speeds seemed to stay constant while the system was being calibrated... which took over half an hour.

And yes i put thermal paste on the CPU's, arctic silver FTW! ;D

 

[sabot]

ASD puts the machine under Massive Load, its the only real way to fully test all parameters ;D


but then it would be as its apples own test software as used in their worksops