Wire of the fan is disconnected.

Check if the wiring of the fan is connected with the signal backplane. See reference 1 image.

Blocked fan.

Unblock the fan. Ensure that the fan can turn freely. The DMD fan of the Blue channel is located above the Light Processor and Light Pipe. See reference 11 image. No need to remove the Light Processor to access the fan.

Damaged wire unit.

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

Fan end of life.

Replace the fan. See service manual chapter "Replacement of the fan of the Red channel".

Malfunction Cinema Control board.

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

Other fans are also not spinning.

Replace the SMPS Board. See service manual chapter "Switch Mode Power Supply (SMPS)".

Defect Signal Backplane

Replace the Signal Backplane. See service manual chapter "Card Cage".