The motor does not turn at all, how do I check it step by step?
Work from source to load: battery, fuse, supply terminal, chassis return, command input, driver output, motor. Always take the measurement under load.
Work through the check from the source towards the load: battery voltage, fuse, the voltage at the driver supply terminals, the input command signal, the driver output voltage and finally the motor. Measuring under load is critical; if a system that shows 12.6 V at rest drops to 9 V when the command is given, the problem is not in the motor but in the wiring or in the battery itself.
The ordered checklist
- Battery / source voltage: Measure it at rest and at the moment the command is given. If there is a serious drop under load, the battery is weak or the cable cross-section is insufficient.
- Fuse: Visual inspection misleads; measure continuity across both ends.
- Driver supply terminals: Measure the voltage on the terminal itself, not at the battery post. The difference between the two shows all the line losses. If the reading is low here, look for the fault along the line.
- Chassis return: Measure the voltage between the driver chassis terminal and the battery negative post under load; more than a few hundred millivolts points to a bad return connection.
- Input command: When the button is pressed or the remote control is used, does a signal appear at the relevant input terminal (IN1–IN4 on the KS250, A–D on the PT500)? If you are working over RF, verify separately that the receiver is powered and producing an output.
- Driver output: Measure the voltage at the motor terminals while the command is applied. If voltage is present and the motor does not turn, the problem is in the motor or the mechanics.
- Motor: Apply supply directly to its terminals briefly. If it does not turn, the motor or the mechanics are seized.
What each measurement tells you
| Measurement point | Expected | What a deviation means |
|---|---|---|
| Battery post, at the moment of command | A steady supply | If it drops, the battery or the main cable |
| Driver supply terminal | Close to the battery post | A large difference means line loss, a loose connection |
| Input terminal with the button pressed | The command signal is there | If not, the button, the cable or the receiver |
| Motor terminals, at the moment of command | Output voltage present | If present, the problem is in the motor or the mechanics |
This fault isolation logic splits the line down the middle: every measurement settles which half the fault is in, and no guessing is needed.
Common mistakes
A reversed polarity connection, a loose terminal, the current limit pot set close to zero and the movement already resting against its end stop are the most frequent simple causes. And then there is measurement error: holding the multimeter on an unloaded circuit and saying "there is voltage" misleads, because a voltage drop only appears while current flows. Touch the probe tips to the conductor itself, not to the terminal screw; a reading taken over an oxidised screw head hides the real contact resistance. Forgetting the chassis return is a classic too: with a flawless positive line, if the negative is taken from under a painted panel the system collapses under load.
Where this list is not enough
The list is for the case where the motor does not turn at all. If the motor turns one way but not the other the fault lies elsewhere and a single-direction fault follows a different check. Symptoms such as intermittent running, stopping as it warms up or sticking at a particular position cannot be found with this list either; for those, look at the symptom-cause-measurement matrix.
What to do
Work through the steps in order without skipping any, and note every measurement; the fault usually shows up in the difference between two neighbouring measurements. When you find an unexpected value at a step, do not skip the rest of the list — put that point right first and then repeat the measurements from the beginning.
The full topic: DC Motor Driver Selection Guide