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OS X - Development and Darwin Discussion and questions about development for Mac OS X.

iMac G5 fan control

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Member Since: Jul 18, 2008
Posts: 1
apple_fan546 is on a distinguished road

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Hi all,

I'm new here so I'm not sure if this is the right section to be posting my question in, but I figured this was the best place to put it. Here's my dilemma

I have an iMac G5 17" 2.0Ghz (Rev.B). For the last 2.5 years, it's served me well. Over the summer when it got warm, I took notice to how loud the main CPU fan was getting when I put a significant amount of load on it. Encoding DVDs with iDVD was particularly bad. Yet, no problems (shutting down, kernel panics, etc...), just a loud machine. A week ago, I started monitoring the temperatures in my iMac and that's what pushed me to start tinkering with my system.

Just to give you and idea of the temps I have going on, according to 'Temperature Monitor', the CPU temp hovers around 180 F when under load and around 150 F when idle. The processor performance is set to "Automatic". If I set it to "Highest", it idles around 165 F "Reduced" is 140 F. Even more alarming (to me at least), was how hot my hard drive was getting. I found it occasionally reaching close to 140 F!! An hour of research online and it turns out the HDD temp sensor is mounted in a really bad position. Hmmm... I opened up the iMac, pried the sensor loose. then reattached it directly to the HDD itself. Now the HDD only gets up to 130 F, but that's still WAY too hot. I'm actually amazed it hasn't failed yet (knock on wood).

First, I looked into re-calibrating the iMac's thermal threshold for both of the sensors... i.e. - when the fans began to ramp up from idle, and what the max temperature is that they are supposed to keep the CPU and HDD at. A few more hours on the internet turned up nothing. I also found out that the common SMCFanControl app used to set minimum fan speeds on intel macs doesn't work on PPC-based macs because they don't have an SMC. Some of the later PPC-macs have an SMU, which is in charge of controlling the fans and monitoring temperatures, but so far I haven't figured out a way to get into it and modify it.

Then I discovered this "solution" that involved changing values in some kernel extension files (.kext) so that the iMac would begin to spin its fans up at a lower temperature. This is where I'm currently stuck. The two files I have been playing around with are titled: "AppleFan.kext" and "AppleBlower.kext". I found several different sets of instructions on the web, but none of them seem to work. I am able to log in as "root", change the "fan-speed-table" in the "AppleFan.kext" file, but after I restart, nothing changes. The iMac still heats up to 180 F under load and idles at 150 F. I've even tried repairing disk permissions before and after restarting, to no avail. It looks like there could be several other .kext files that could play a role in fan control, but I'm not sure what to modify in them. In the "AppleHWSensor.kext" file, there are several "dictionaries" within the file "info.plist" that are somehow related: "ControlTypeFanPWM", "ControlTypeFanRPM", "SensorTypeFanSpeed", but I have no idea what to do from here.

Someone with more knowledge than me have any suggestions?

Thanks in Advance,
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