Abstract: An apparatus that detects the occurrence of slack in a cable and that compensates for detected slack is disclosed. The apparatus includes body parts that are movable relative to each other between fully extended and fully retracted positions. A bias device biases the body parts toward the fully retracted position. However, normal tension conditions in the monitored cable overcome the bias and extend the body parts to their fully extended relation. If the cable becomes slack, the body parts retract to take up the slack. If the cable slack is to such an extent that the body parts move to a predetermined relative position, the apparatus generates a signal warning of extreme slack conditions. The present invention also is a cable slack control apparatus for a door operator, with such control apparatus including a cable slack detection and compensation device and a door motor drive control device.