look for the swashplate, it's about as big as your thumbs, has two balls on it for the servo's to connect to, should be just below your lower blade... this should be one piece of plastic, you should not be able to see the bearing, and the top "hat" looking part should be seated down inside the swashplate with the outer shaft going through it..

if you flip it with your fingernail and the thing rattles and comes apart, you either need a new one or glue the one you have.. compare them between the two heli's..