Zenith z50px2d I have a friend who gets good sound but sometimes no picture. If he taps the side of the tv it sometimes brings the picture back. he wants $500 for the tv as is. Is it worth fixing? The unit is only 13 months old.

Check your input connections, especially the HDMI (if in use). I have found through personal experience that the weight of the cable and any small vibration can be enough to loosen the connection and leave you a blank screen. The manufacturers would have been smarter to have all the inputs face toward the floor at the bottom of the set (like the power cord). Anyone who has mounted their set to the wall will understand what I am saying.
That being said, you may be better off saving your money and buying a new LCD TV. The Zenith sets have proved to be a ticking bomb. If you Google "pop" and "z50px2d" you will read a number of posts on various boards that indicate that the Zenith plasmas have about a 2 year life expectancy before they are in need of some very expensive service. And frequently even after they are serviced are prone to further failure.
Someone pointed out to me not to long ago a valid fact: LCD technology has been around since the pocket calculator and therefore much less prone to unexpected failure than the relatively new plasma technology. I just wish someone had told me that 2 years ago when I ponied up $3000 for my Zenith z50px2d that blew out a few days ago.