Did you have a problem restarting the dryer after each use? It could be a bad motor or open contact in the timer.I would also check the wiring harness and the plug going to the motor. Hope this helps
You mean ALE643RBW... drew blanks when I first looked and gave up. So... there's no moister sensor for this model. It runs the cycle by the start point of the timer. Its labled "more" dry or "less" dry in some fashion which merely changes the length of the cycle. Simple and dependable but doesn't meet todays "green" requirements.
Most likely it is the timer which lists at ~$170US from Sears. Your dryer has gotta have some years on it so not sure what else it may need in the near future. If you can do repairs yourself, $80 refurb timer on Ebay Otherwise to pay labor and markup... better off with new.
Always check the breakers in your electrical breaker box in house first. I say this because it takes 2 for dryers one for coils and lights the other for motor and thermostats. Next check door switch by listening for contact click sound when you push the door closed if you hear it switch is good and most likely motor is bad.
Over the years I've found that if it buzzes but will only start when you "assist"it, the drive motor is at fault. The hot smell you describe backs that up.. This assumes the idler is ok and the belt is routed correctly. Make sure the belt is on the motor pulley and not riding on the motor shaft. This can happen sometimes if you have to install the belt by feel when you can't see it well . That said, the motor should still start without assistance even with an incorrectly installed belt. Good luck