Failures of the stepper motor itself are generally manifested as burnout of one or multiple phase windings (coil short circuit or open circuit). This type of fault can be diagnosed by measuring the DC resistance of the motor coils with a multimeter and comparing the readings with those of intact coils. (In most cases, not all motor coils burn out simultaneously; at least one or several groups remain functional.)

For motors assembled with screws, the housing can be disassembled directly using screwdrivers and pliers. If the housing is welded, carefully take it apart with a file or hacksaw. Avoid prying forcibly to prevent deformation.

After disassembly, the internal structure of the motor can be inspected. If one or two phase coils are burnt out but the coil bobbin remains undeformed, new windings can be wound manually according to the original wire gauge and turns.(When removing burnt coils, count the number of turns accurately and measure the wire diameter of the removed enameled wire with a micrometer. Since the insulation coating thickness differs between imported and domestic enameled wires, burn off the insulating varnish with a gas lighter before measurement. The same measuring method applies to replacement wires.)

If the bobbin is deformed, it must be replaced. If a matching bobbin cannot be obtained, a similar bobbin can be modified. Alternatively, a new bobbin can be fabricated from high-temperature resistant flame-retardant insulating materials and bonded to replicate the original shape.

After winding, reassemble the components carefully. Rotate the motor shaft by hand; the assembly qualifies if there is no obvious jamming.

It should be noted that if a stepper motor fails, the corresponding stepper motor drive circuit must also be inspected for damage before replacing the motor.