Temperature Control Issue on a Power Mac G5

[Antoniente]

Hello everybody,

I have a Power Mac G5 Dual-Core 2.3 GHz (Late 2005) bought in April 2006. A couple of weeks ago I decided to clean the dust accumulated inside 4 years so I proceeded to disassembly the system, removing almost everything (motherboard, processor, superdrive, hard disk, power supply, etc). After reassembling it I did a "Thermal Calibration" using an Apple Service Diagnostic disc (ver. 2.6.3), the only indication I didn't follow was that the room temperature was 29ºC instead of 25ºC or less. The system works perfectly but for some days I've noticed that the processor's temperature is too high (up to 70ºC) and the fans don't help (they are always at the minimum RPM with slight variations, below 600 RPM, totally inaudible). Before performing the cleaning, with the same room temperature, the processor didn't go above 60ºC because the fans rose its RPM's whenever the processor reached that temperature.

 

Any ideas? Thanks.

[cbreaker]

You did add thermal compound to the CPU when you re-installed the heat sink, yes? If not, then that's your problem. Thermal grease will harden after it's gotten up to temperature and stayed there for awhile. You can't re-use it because it won't create a heat-seal between the CPU and the heat sink.

 

You need to completely clean both surfaces, and then clean it even more with a fine cloth and a small amount of rubbing alcohol to remove any grease from fingers or leftover compound.

 

You should only use a high quality thermal grease like "Arctic silver" brand grease. Any of the look-alikes will work ok too - it's silver/grey in color. The Radioshack white stuff won't be enough.

 

- Spread a very thin layer onto the CPU. Use a rubber glove or wrap your finger in plastic wrap to do it. You don't want grease from your skin to get on it. Spread it evenly and very thin.

 

- Spread a similar layer on the heat sink, only on the area that touches the CPU.

 

- Install the heat sink, and once it's clipped into place, slide it back and forth (just as much as the clip will allow without using much pressure) in order to create a nice air-free bond between the surfaces.

 

Heat sink compound is great at transferring heat, but not as good as the two surfaces touching each other directly. So, the grease is only really used to fill in the gaps and imperfections between the surfaces.

 

If you follow those directions exactly, your CPU may even be cooler than it once ran before.

 

As for the fan speeds, well, I don't know. Maybe you plugged them into the wrong fan ports (probably not) or the temperature might not be hot enough to warrant faster speeds. But, 70 degrees Celsius is awfully hot, but those processors run hot. 70 might not be the end of the world.. try running a CPU stress test and check the temp then.

 

Of course, if you followed all these directions already (I could be way off base here) then it's got to be something else, and I wouldn't be sure what it was. But, from my experience when this happens it's because there's a bad bond between CPU and heat sink.

 

Next time, your best bet is to leave the heat sink in place, and if you really need to clean the fan or something, unscrew it from the heat sink. If you have a good heat bond between the CPU and heat sink, you really don't want to mess with it. Generally speaking, a decent can of compressed gas or two is all you need to completely clean out a really dusty PC. You just might want to bring it outside to do it =)