Disconnect power first  In order to test and effect repairs on any product, you must be able to disassemble and reassemble the appliance. So lets start with disassembly on this dryer. Unplug the dryer. Get the top up by pushing in on 2 clips on either side as shown in this picture. We need to remove the front of the dryer next. There are 2 or 4 screws inside at the top on most of the older dryers that we need to remove. Once the screws are removed, you can pull forward on the front and lift the complete  front off the 2 clips on the bottom of the dryer. Unplug the door switch wires and set the front aside. Next step in disassembly is to remove the belt from the idler and the motor pulley. This is done at the rear of the dryer. Remove the 2 screws holding the inspection plate on the left rear of the dryer. Remove the plate. Look carefully at how the belt threads around the motor pulley and idler pulley so you can replace it. Remove the belt from the motor pulley. Return to the front of the dryer, grasp the belt in one hand and the front of the drum in the other hand. Lift up on the rear of the drum and pull forward with the other hand. There is a ball on the rear of the drum that rides in a socket located in the center of the back of the dryer. You are lifting the knob up and out of the socket. Look in the center of this picture for the socket. You have taken the dryer  far enough apart at this point so that you can accomplish any repairs needed on this style dryer. It is not necessary to go this far for all repairs, but if you need to disassemble, you have the information.