Zenith Z50PX20 I've been told we need a new plasma screen that would cost twice as much as the orginal tv. The tv made a popping sound, and then the screen looked like a photo negative. If we still have some picture, is it possible there is another problem other than the plasma screen?

these can be a bit costly. I would call around and get a few prices. It maybe cheaper to buy a new set.
good luck

Its not the CRT, its the Y Sustain board.. This happened to mine 30 minutes ago.. and has happened to every owner of a plasma tv that uses the toshiba Y Sustain board..

Please take the time (5 min) to file a complaint with www.consumeraffairs.com...you will see that you are not the only one with this exact same issue on this zenith plasma model Z50PX2D:
http://www.consumeraffairs.com/search.html?cx=partner-pub-0200629403145096%3Aqt7mbbqybbg&cof=FORID%3A10&ie=ISO-8859-1&q=zenith+plasma+#1124

could be bad capacitors in power supply. 

Did You Enter 0000 As The Code?

Thin lines down center of ESA 42"plasma tv, about 1 pixel wide each, about 3/4" to either outside line
Started as 1 then 4 over 4 months

It might be one of the power supplies. There are three in this model. One for the sound, one for the video, and one for the computer components. The video power supply is probably shot. They cost about $200 a peice from LG. If there was a "pop" sound when the video stoped, then it might be one of the circuit boards in the back. Yet again, they are three, each costing around $200 from LG.

Hey - when my screen did that I was told that my Y & Z sustain boards blew out. I now have another issue w/ my set & I was told by a tech guru on this site that there are additional boards that should have been replaced as well.

I too fee like I want to take a crack at fixing it myself, but I don't know specifically which parts to address.

I complained to Zenith (in a nice way) & they've extended my warranty to fix my new problem free of charge, which they should do anyway

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.

This just happened to my Z50 yesterday...10 days after it came back from the repair shop! The first repair was for the "popping" problem where the tv makes a loud pop and the screen goes black. This took 6 weeks to get fixed. For this new problem the repair center is getting hold of LG to find out what to do. I am also calling them because I see this is a major problem that people have been experiencing out of warranty. The first customer service rep told me I was out of luck but I am not accepting that answer. Good luck, we'll both need it.