I have a c. 1958 Lionel F Unit. When I put it in the track, the headlight lights, but it just buzzes and won't move. When I move the E Unit lever under the locomotive (which I think takes the 'E unit' out of the circuit), I get the same buzz and no movement. When the locomotive was last put away perhaps ten years ago, it ran. I know the tack is wired correctly because my other Lionel locomotive from the same era runs fine in both directions. What's up here? I've read on the Internet how to test the motor(s), but I don't understand the connections being AC and all. My power pack is a Lionel Type S, which dates from 1947 I think. It has four posts -- A, B, C and U. Photos attached. I identified posts on a motor 1, 2 and 3 to make the process clearer to me. Thanks y'all.