Locate the affect transistor (Channel PWM 1 or 2)

Note: This is a quick guide. It makes the assumption that the transistor is dead no matter what. This guide does not provide analysis and help on NPN transistors as it is not needed for getting the fan back to work.

Before you continue, you might want to read on SMD soldering from different sources (iFixit or see the provided On Semi guide on SMD, which looks very comprehensive or Sparkfun's Guide can be highly recommended) and plan time if you haven't got the environment already setup