Dc motor speed controller down for many reasons, so in order to solve the downward speed need corresponding processing for the cause of the problem. 1. Cage rotor broken bar. If is the screen cage rotor broken bars, so in the operation of the motor controller in its stator current meter pointer will swing back and forth, sometimes there will be a spark, and hum. In this article need to break the detector or iron powder method to find the article break fault place, then go to the corresponding methods of repair. 2. Low voltage power supply. Input voltage of dc motor controller, check, if it is found that the power supply voltage is too low, then to adjust the supply voltage. 3. The stator winding of motor controller connection errors. If the normal operation of the dc motor controller of stator winding wiring connection method is D shape, but in fact become Y connection, after the discovery, should make the correct in a timely manner. Above is the processing of dc motor controller speed dropped, you know.