the first thing to do is see if you have another mic first, to fit the rig, then you could alway's if that dos not work, ( you might think im joking but i am not,) smell the back of the rig where the pl259 goes in and see if you smell burning or burnt smell, that indicates something went pop, if after both of them test's your still at square one, you could always watch video's on repair's and give Lamco cb centre a bell and see if they know of anyone who repair's rig's, they will give you a guys name called david, from newport he fixes rig's very well, he did all mine and they are very good, heres a video on the grant's,
https://www.youtube.com/watch?v=jN6uc-Kpetw