Small Cooling Fan What reason can not start

   "Small Cooling Fan" Unable to start the boot that boot through fan does not turn, need to hand pull force or about to turn up, this is what causes it? The industry we call this mini fan has dead spots or dead. Typically "Small Cooling Fan" has four poles, we call four pole brushless fan, four poles in the middle of this is the weakest magnetic force, so easy to stop does not turn, the cause of the fan does not turn as follows
1. Driver IC induction poor
2. Driver IC with corresponding positions deviate silicon steel
3. "Small Cooling Fan" too far away from the rotor magnetic stripe IC