I have a couple of Hs 81's that I changed to metal gears on, when I put the servo arms on at 90* turn on the radio and power to the rx and move the stick up on the radio the servo arm returns to 90, when I move the stick down and back to center the arm moves past 90 and stays there. I have tried it with 2 different receivers a berg and a futaba, and 2 different radios a 9C and a T6xhs. Anybody know what the problem could be?