The motor turns one way but not the other: what could be the cause?
If the motor runs in one direction but not the other, the problem is almost never in the motor. Check in order the input signal for that direction, the current limit setting for that direction, mechanical binding and finally the corresponding half of the bridge. Measuring the inputs before removing the motor saves time.
Systematic diagnostic order:
- Verify the input signal. On the KS250, IN1 is clockwise start, IN2 is reverse start, and IN3 and IN4 are the stop inputs for the respective directions; on the PT500 the A, B, C, D digital inputs are used. Measure whether a signal appears at the input terminal of the non-working direction when the command is given. A broken wire, an oxidised button contact and the relevant RF receiver output not working are the most common causes.
- Check the current limit. On the PT500 each direction has its own limit: clockwise is set with pot A1 and reverse with pot A2. If the pot for one direction is set too low, the movement is cut off as soon as it starts; from the outside it looks as if it does not work at all.
- Check the mechanics. Remove the load or try moving it by hand in that direction. A slide binding in one direction, a tangled rope or a mechanism resting against its end stop are typical causes.
- Power the motor directly. Connect the battery directly to the motor terminals briefly and see that it turns in the reverse direction; if it turns, the motor is sound.
- Assess the driver. If all of the above are clear, one half of the bridge may be faulty; in that case the module must be taken in for evaluation.
When measuring, secure the load mechanically and assume that the motor may move suddenly.
Full topic: DC motor and driver fault diagnosis matrix