Nexstar SE: Old engine starts running uncontrollably

Product Description
Pressing one of the Alt keys on a Nexstar SE mount caused the motor to run uncontrollably.
Only by completely shutting down the mount could the movement be stopped.
We first performed a factory reset and a firmware update.
Neither of these actions resolved the issue; the motor continued to run uncontrollably after pressing the Alt keys.
We then replaced the hand controller. The problem disappeared afterward.
To confirm our suspicion that the hand controller was the cause, we connected the supposedly defective hand controller to another Celestron mount.
Amazingly, the HC worked perfectly here, without any issues.
We haven't been able to definitively determine the cause of the problem—what is certain is that the mount is functional again with the replaced controller.
We also loosened the permanent Alt clamp slightly, as it was very cumbersome. To do this, remove the plastic cover on the back of the mount and loosen three screws.
Using a socket/ratchet, carefully loosen the nut that's screwed onto the main axle.