I had an issue with my then 2 year old 5500. I was testing it to try and find the issue and I noticed the motor was running , but not moving the antenna. My problem was the dreaded drive gear set screw loose issue. I had to almost completely take the rotor apart to get to the set screw on the drive gear to tighten and apply some loctite to it. It's been working fine now for 5 years or so. Before you take it down to work on test for this...

73 Jeff kb2m