iFixit

If replacing the motherboard transfer the four thermal pads on the underside of the motherboard to your new motherboard.

Motherboard remains.

The DVD drive and the motherboard are "married" when they leave the factory. If you replace one you must replace the other or make sure that the keys match. If you put any old DVD drive onto a motherboard that it is not "married" to it will only play DVDs, no games.

Before heating up the motherboard, be sure to clean the old thermal paste off both the CPU and GPU until they are as clean as the processors seen in the first picture. The process for cleaning the processors can be found here.

Lay the motherboard with the processor side facing down on the flat metal bottom of the the bare chassis (with its open side facing down) as seen in the second picture. Allow the tall USB socket to hang over the edge of the chassis so the board sits flat.

Use a heat gun on the LOW setting to heat the entire back of the motherboard for one minute. Be sure to continually sweep the heat gun back and forth across the face of the motherboard to evenly heat it.

After heating the back of the motherboard for one minute, flip the motherboard over and lay it on the chassis as shown.

If you have installed the RROD fix kit already, keep the two small black heat sinks included in the kit stuck to their respective chips. The tape that is used to attach them to the chips on the board is extremely strong and attempting to remove them may damage the chips underneath. The heating process will not damage the heat sinks in any way.

With your heat gun set to HIGH, evenly heat the area boxed in red for four minutes.

When using the heat gun on high, it is extremely important to continually move the heat gun so the stream of hot air evenly heats up the desired area.

Avoid directly heating the many cylindrical electrolytic capacitors located near the area boxed in red.

After heating the area boxed in red for four minutes, turn off your heat gun and allow the motherboard to cool down to room temperature without moving or disturbing it in any way.

At this point, we strongly recommend installing our Red Ring of Death Fix Kit to safeguard against future failure.