I have had the same problem as you in the past, all radio functions but FM. I had removed radio and opened up the bottom cover and adjusted the tuning pots while turned on and got the FM working again. But after a few weeks it failed again. This time I bought a spare radio and sent the broken one to Sierra for repair. At the same time had the aux input added. Reinstalled original radio and all has been fine for almost 2 years. This can be a common problem on some of the 1500 radios. Cost to do mine was about $150 total. Hope that helps and you get it all back in working order. Mike
This seems to be a systemtic problem with the GL1500 radio.. with solder joints and board problems around the coils in the FM section... I've had mine back tothe shopa couple of times and it still has issues..