How to tell if the tv is going bad?

If the brand names are Muntz or Dumont or Silvertone it's a good start. ;) Seriously, it really depends on the quality of the picture and if it's operating reliably. Soon (Feb17th. 2009) you'll have to have a digital converter to be able to use the older sets, or a cable box or satellite receiver. That's another indication that your set is getting to be on the old side. If it's working OK and you're not ready to purchase a new set, then don't. If you're looking for an excuse to get a new one, then just make the statement that your TV's getting too old and it's time to replace it.