Malfunction Fan Control board or SMPS board.

Measure on the Signal Backplane the ++12V voltage on pin 1, 2 or 3 of the connector of the black wire unit which comes from the SMPS board. See image.

If the measured voltage is about 12V then replace the Fan Control board. See "Removing a board in the card cage". Otherwise replace the SMPS board. See "Replacement of the Switched Mode Power Supply".

Short circuit or bad connection.

Check the Signal Backplane for bad connections.