1. Cause of failure (1) The rotor winding has a broken circuit (one phase disconnected wire) or the power supply loses power at one phase; (2) The beginning and end of the winding lead line are wrongly connected or the internal connection of the winding is reversed; (3) The power supply loop contact is loose and the contact resistance is large; (4) The motor load is too large or the rotor is stuck; (5) The power supply voltage is too low; (6) The small motor is too tightly assembled or the grease in the bearing is too hard; (7) The bearing is stuck. 2. Troubleshooting (1) Identify breakpoints to fix; (2) Check the polarity of the winding; Determine whether the winding end is correct; (3) Tighten the loose wiring screws, use the multimeter to determine whether the joints are falsely connected, and repair them; (4) Load reduction or detection and elimination of mechanical failures, (5) check whether the specified surface connection method is mistakenly connected; Whether the voltage drop is too large due to the too fine power supply wire, it is corrected, (6) reassembly makes it flexible; Replacement of qualified grease; (7) Repair bearings.