One of the motor is dead and already purchased a set of spares from the net
Warranty does not cover accidents. If that Tello is his son's, then most likely than not, it suffer a crash.Is the Tello still under warranty?
If not, take a look at this thread.
There's a bunch of tutorials out there, just wanted to share my experience! :) I followed this video which is the one I liked the most (it's funny and clear): He accidentally cuts off the wifi antenna haha but that's good for us because now we know which wires to stay away from. This is the...tellopilots.com