When the motor is turned on, it makes a strange sound but does not turn at all, which is a very typical fault phenomenon. It usually means that the motor itself or its drive is mechanically jammed, or there is a problem with the circuit. Safety first, be sure to keep in mind: before any inspection operation, the power supply must be completely cut off to strictly prevent the risk of electric shock!

The following are the main triggers of the failure. It is recommended to troubleshoot step by step according to the principle of 'first easy and then difficult' to improve the efficiency of diagnosis.

I. Mechanical reasons (the most common)

When such problems occur, a dull "buzzing" sound can usually be heard, and the heating speed of the motor will be significantly accelerated, which can be used as a preliminary judgment signal.

1. Bearing damage: This is one of the most common causes. The lack of oil, wear, rust or breakage of the retaining frame of the bearing will cause the rotor to be stuck or with great resistance to rotation. The sound is usually a friction sound of "clicking" or "shatling".

Judgement: After the power is cut off, try to turn the motor shaft by hand. If it can't be turned or it's very hard to turn and there's a feeling of jamming, it's basically certain that it's a bearing or mechanical jamming.

2 Load jam: The motor itself is running normally, but its connected related devices (such as pumps, fans, gearboxes, compressors, etc.) are stuck.

Judgement: Disconnect the connection between the motor and the load equipment, such as separating the pump impeller, fan blade and electricity. If the motor can idly normally after detaching, then the problem is in the load equipment.

3. Sweeping: that is, the friction between the motor rotor and the stator inside. This is due to the serious wear of the bearing, the rotor sinks or is eccentric, and the stator core is scratched when rotating. It will make a very harsh friction sound.

II. Electrical reasons

Such problems are usually accompanied by a sharper and louder "buzz" sound than during normal operation, which is a manifestation of excessive current.

1. Power supply phase missing (for three-phase asynchronous motors):

Reason: One phase of the three-phase power supply is out of power (the fuse is burned out, the contactor contacts are burned out, the line is broken, etc.). The motor will make a "buzzing" sound but cannot be started, and it will heat up seriously or even burn out in a short time.

Judgement: Use a multimeter to check whether the three-phase voltage input to the motor wiring is normal and balanced. This is one of the most common faults of three-phase motors.

2. The starting capacitor/single-phase capacitor operation failure of the starting motor:

Reason: For single-phase motors such as household fans, washing machines and small pumps, the starting capacitor is the key component to obtain the starting torque. Once the capacitor fails (capacity reduction or broken circuit), the motor will be unable to run due to insufficient starting torque and only a "buzz" sound.

Judgment: The capacitor drum bag and leakage are obvious signs of damage. It is necessary to use a capacitance meter to measure whether its capacity is consistent with the nominal value.

3. Winding short circuit or burning:

Reason: The motor winding is partially short-circuited or ground-to-ground short-circuit, resulting in an imbalance of the magnetic field and the inability to generate effective torque.

Judgment: Smell whether there is a strong burning smell. Use a multer to measure the winding resistance (the three-phase winding resistance value should be basically balanced) and insulation resistance.

4. Wiring error: Cause: For example, the star/triangle connection of the three-phase motor is wrong, or the internal wiring board is off. 

III. Comprehensive troubleshooting steps (for reference only, specifics need to be adjusted according to the actual situation of the equipment)

1. Manual rotation after power-off: Make sure that after power-off, try to turn the motor shaft by hand.

Can't turn -> Focus on checking the mechanical part (whether the bearing and load are stuck).

Turn flexibly -> The problem is likely to be in the electrical part.

2. Disconnection of the load: separate the motor from the load and test run the motor separately.

No-load energy transfer -> The problem is in the load equipment.

No load and no rotation -> The problem is in the motor itself.

3. Basic electrical troubleshooting (professional operation ability is required):

Power detection: Use a multimeter to measure whether the power supply voltage is within the normal range, and check whether the three-phase power supply is out of phase.

Capacitance detection: For single-phase motors, first observe whether the appearance of the capacitor is bulging, leaking and other abnormalities, and then measure its actual capacity through the capacitance meter.

Check the winding: measure the winding opening and off, the balance of the resistance value and the insulation resistance to the ground.