It is possible that the transistor is damaged or there is a problem with the fan itself.
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You can use a multimeter to measure whether the triode of the control fan is damaged, if the tube is not damaged, it may be the fan itself is damaged, you can pull the fan off the circuit board, and connect a 12V direct current (pay attention to the positive and negative electrodes), to see whether it is rotating, but also to see if there is no foreign matter stuck. If you swing the fan wire a few times, the fan will turn, it indicates that there is a broken wire or poor connector contact inside the wire. If it still does not rotate, the fan will fail. For the charger using intelligent heat dissipation, in addition to the above checks, you should also check whether the thermistor has poor contact or damage, welding, etc. However, it should be noted that this thermistor has a negative temperature coefficient and should be paid attention to when replacing it.