Blocked fan. (reference 4 of image "SMPS fans connections")

Unblock the fan. Ensure that the fan can turn freely.

Damaged wire unit. (reference 3 & 5 of image "SMPS fans connections")

Check if the wire unit of the fan is not damaged. Repair if possible, otherwise replace with new one.

Malfunction Fan Control board.

Replace the Fan Control board. See "SMPS compartment fans".

Fan end of life.

Replace the fan. See "SMPS compartment fans".