Text basically taken from this RCgroups post

Docu for repairing defective FETs on the H101/H8S board (pictures). Maybe it's interesting for you guys. If one has a broken FET one could re-use a FET that's intended for inverted flying, in case one doesn't use that. Identify the defective FETs with an oscilloscope, but should be possible with a multimeter, too. If you give full throttle (in acro mode) and both PINs of one motor are 0V then the A1SHB FET for normal mode of this motor should be defect. If it's ~4V then the A0SHB FET should be defect. Maybe someone can confirm that.