Dane from Transistor Man had a Macbook Pro with a GPU that wasn’t working. The system would boot but the display output was dead. Similar to the Xbox 360 BGA problems there are some Macbook Pro computers that have experienced BGA solder issues. The big issue here is that BGA devices have the solder connections under the device itself. Dane used a heat gun and a variac to blow a measured amount of heat onto the device to reflow the solder in attempts to repair the bad connections. The actual remelting of the solder isn’t a quick application of heat as it is when you solder a through hole solder pad. To prevent thermal shock you need to slowly bring the part up to temperature using the typical temperature profile that is normally used to reflow parts.
Read here How to Reflow a Macbook Pro GPU.
