Here are the usual suspects for runaway slews that should be checked if you have this problem with your CG-5 mount.
Power supply: make sure you have a good one or replace it. Try a different type of power – swap an AC adapter for a car battery source. Check connections, including the power jack of the telescope.
Cables: try massaging to work out kinks. Check the jacks for cleanliness or bent pins. These tips apply to both the DEC cable and the hand control cable. Try replacing the DEC cable.
Internal loose connections. Check to make sure the boards and jacks are well connected inside your RA and DEC motor housings.
If none of these tips work, the mount probably needs factory service or parts from Celestron.