SCI: Lighthouse: Voltaic Bathysphere using keyboard arrow keys locks motion
In the original game you can use the keyboard arrows keys to move the bathysphere up and down and the arms left and right, probably. It should move as long as you are holding down that arrow key.
If you do this in scummvm then it will go in the direction you select and then lock. You can get the arm to work again using the left lever, but not the right lever.