hi neil there could be a number of things to check 1 st being that all the ends are secure in the receiver box 2nd could be that the servo has broken 3rd could be that you mite of had a wack on the front and you need to take the servo saver off and reajust the trip before re assembleing it also the servo horn could be stripped inside
Personaly what i would do it remove the servo saver and see if the servo is working then if its not then id say you need to replace it
Hope this helps