What is the cause?

The motor does not run, but when you use your hand to press the shaft, it works normally

Hello tt3.hatrunglam,
I’m not clear at what you mean by “when you use your hand to press the shaft, it works normally”, could you clarify a bit more on this? I ask as the behavior of the motor while hooked up will help determine what components are most likely the cause.

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Hello tt3.hatrunglam,

Yes, intermittent problems can be very difficult to troubleshoot.

Please provide a little more information about your system to better help this community to help you.

You mentioned pushing the shaft or the motor, yet you provided a picture of the PCB.

Judging from the picture, you have a 3-phase brushless DC motor. This motor may or may not have what are know as Hall effect sensors to detect the rotor’s position. This leads me to think that:

  • the motor may have a loose connection in the heavy power wires leading from the circuit board to the motors stator windings
  • there is a broken or loose connection in the Hall sensor circuit.

Another possibility is a broken / cold solder joint on the circuit card.

Perhaps you may be able to perform what is affectionately called “percussive troubleshooting” on the system. It sounds like you are already performing this technique as you “press” on certain things. Using an insulated tool, you can tap on the components until the defective one is identified. Do so with extreme caution as the circuit is live. There is risk of damaging the circuit and yourself if you are not careful.

Again, be sure to use an insulated tool.

Be safe,



I have to agree with APDahlen, but also the obvious question is; is your motor bad or getting weak?


Hello, the motor is still working normally, the problem is in the electrical circuit

I use my hand to rotate the shaft, when there is inertia from the impact hand, the motor will operate. Note that the motor still operates normally, the problem is in the electrical circuit

If, once you give the motor an initial “spin” and it works normally after that, then the problem lies with the motor not getting enough power to produce the torque needed to turn. This can be caused by multiple things, however I suggest considering the following:

If the motor has a load and giving it a boost gets it going, and it continues running normally with the load on it, your problem is the initial extra power required to get it running. If that is the case, you might need to check your capacitors as they may not be charging/discharging as intended. Additionally, if there is a load on the motor, try removing it and see if it still requires the manual boost.

If the motor has no load, and after you get it running from the initial rotation by your hand it will stop again if you put any sort of load on it (including slowing it down with your hand), then you’re most likely encountering an issue of the motor not getting enough power. If this is the case, I suggest measuring the outputs of the driver and working backwards from there.

Typically, with DC motors torque is inversely related to speed, so I find it odd that it continues working after you’ve ‘nudged’ it a bit, as it should have the most torque near resting state. I think APDahlen’s suggestion for troubleshooting might be the most effective route at this point.


Hello tt3.hatrunglam.

Can you share a picture of the motor?

This is sounding more like a defective capacitor in a capacitor start / run AC motor. I may have misunderstood your situation with an incorrect assumption about the driver circuit.

Thank you,


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