Examine the connector  on the Maincon PCB. Make sure it is not damaged.
Examine the cable. Look for signs of damage or stiffness. The connector  has two housings [2,3] for the cable pins.
Measure the resistance on the encoder cable from leg to leg, and from leg to ground. Make sure each measurement results in an open connection.
Make sure the cable is firmly connected at both ends. Reseat both connections. Make sure the cable is installed in the correct connector at the Maincon PCB.