The video below describes the troubleshooting of AC servo drives. This video goes through visual checks and static checks of the AC servo units. These procedures are applicable to all types of servo drives.
It is important to make sure that visually nothing appears burnt or broken. The smell is also important. If anything smells burnt but cannot be visually seen as burnt, take caution! There may be burnt components in the power section or base of the drive that is hard to see without full disassembly of the drive.
The static check should be performed with caution as well, as it requires using a multimeter to test the different components inside the drive. In this video, Rob explains the exact procedure step-by-step for statically checking the diodes and transistors. Make sure that before performing any static checks that the power has been removed from the drive and the unit has been properly discharged.