MDD
OSX Fan Extension Mod
**
DISCLAIMER **
Altering
any part of your OS or computer will void your warranty and
may damage your computer. These modifications are for educational
purposes only and are performed at the owners risk - This
site or it's owner are not responsible for any damage caused.
Apple
have cleverly built into OS X a system extension that allows
the operating system to control the speed of the main system
fan (and optical drive fan).
A
temperature sensor resides on the G4 processor card which
reads the ambient temperature just under the heatsink. This
temperature data is fed into the OS and a preset number of
temperatures (that reside in the system extension) govern
how much power is fed to the fans IE speed.
By
altering the preset temperatures in the system extension,
we can govern when the fans should speed up, thus allowing
us to keep our system cooler (using higher fan speeds). Some
of you might not like the idea of higher fan speeds as this
causes more noise to emanate from your system. My MDD has
had every single fan replaced (except the optical drive fan)
with quieter ones. For example, the large 120mm PAPST has
been replaced with a Panaflo, the dual 60mm Delta power supply
fans were changed to Verax fans. I have since added
4 more Verax fans to the G4 that run extremely quiet (the
system is virtually silent if it wasn't for the 4 hard drives
- and I mean silent!).
Lets
get to it then. First, you must log in as root to make any
alterations to a system extension. The extension can be edited
using Apple's "TextEdit" application and is found
here:
/System/Library/Extensions/AppleFan.kext/Contents/Info.plist
(Backup
your original extension in case you want to revert to the
original settings)
Scroll
to the bottom of the document and you will find 17 values,
a hysteresis temperature (called "fan-hysteresis-temp"),
and a temperature control curve that lists 16 predefined fan
speeds (a series of 16 numbers called "fan-speed-table").
The
values are multiples of 256 and are in degrees Celsius. For
example 58°C is represented as 14848 (58 x 256 = 14848).
My MDD tended to wind up the fans at approx. 58.5°C and
wanted to reduce this by approx. 3°C. In order to do this
I subtracted 768 (3 x 256) from all the values shown above,
hence 14592 became 13824, 14922 became 14154 and so on. When
finished, save the extension and reboot your system.
The
above CPU temperature reading (shaded) is a combination of
a copper heatsink (from a dual 1.42MHz system), a system overclock
(from 1.25GHz to 1.42GHz), my
fan mod and the extension mod on this page. The results
are fantastic. System temperature is a steady 54.1°C (down
from 59°C) with an ambient room temperature of approx
20°C.
I
have a more powerful system that runs cooler - mission accomplished!
**
Note: This only works on MDD G4's. Future system updates may
override the file with the "correct" numbers. Also,
any errors in the controller extension could cause the system
to overheat, damaging the CPU board beyond repair. **
Additional
information is used with expressed permission from Marcel
Bresink of "Marcel
Bresink Software-Systeme" - a BIG thank you for your
help.
