Blocked fan.

Unblock the fan. Ensure that the fan can turn freely (reference 2image).

Damaged wire.

Check the wire (reference 1image) of the fan. Repair if possible, otherwise replace with new one. See service manual chapter "Replacement of the Light Pipe fan".

Fan end of life.

Replace the fan. See service manual chapter "Replacement of the Light Pipe fan".

Malfunction Cinema Control board.

Replace the Cinema Control board. See service manual chapter "Replacement of the Cinema Controller".