Microsoft Xbox Repair Manual page 83

Once you have thoroughly cleaned the motherboard using compressed air, remove the backing
from the heat sink and place it squarely on top of the chip, continue to put firm (within reason)
pressure on it for two minutes.
Now to take the last step to improve cooling as much as possible we will replace the standard
power source for the fan with a higher voltage one to make the fan run faster.
By using a standard pass through connector such as this one we are able to tap the hard drive
power and connect it to the case fan. By using the power supplies full 12V power as apposed to
the motherboards 7-8 volts we increase the RPM of the fan. The fan blows harder, more noise,
and more cooling.
I know this will make a big difference in the cooling, I don't know if it will fix your system or not.
If you are getting random lockups this will probably be worthwhile at least reducing their
frequency. Each situation is different and some will perform these mods and see no improvement
some will see perfect performance after the changes.
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