I have had an American Flyer 322 smoke in tender Hudson for about 70 years. Two years ago it needed help because it ran very slowly if at all and the smoke bellows had developed a significant tear.
I took it apart removed the armature, cleaned the commutator, installed new brushes, lubricated and reassembled. Armature turns freely by hand But not when powered. Thought it might be e-unit. Replaced e-unit with Dallee electronic e-unit. No go. Dallee unit starts in neutral. Cycling into forward or reverse produces current draw over 2.5 amps, but nothing turns. No current draw in neutral.
AF 312 smoke in tender draws 1.5 amps or less with smoke turned off.
Sounds like a short somewhere.