One thing I recall is our TV having tubes. If the TV stopped working my father would take the back off of the set, look for a bad bulb (or perhaps two) and take them to a store where they had a machine you could plug the bulbs into. The machine would tell you if the bulb was good or not. Once you found the bad tube, you could buy a replacement, take it home, & plug it in. Wala! The TV worked!