Most common problems stem from the solder joints where the tether connects inside. I have tethers that are more than a decade old and no problems. I had one G scale Challenger that just needed the solder joints re-melted. It has been fine ever since, over several years ago that it happened.
Of course, it could be that you accidently damaged something, even connecting something just once. I would bet it's the solder joints though.
