A still picture appeared on the full screen, and it was a picture of a GPS map. Sound was still on. Change channel, screen went black sound went off. I have checked my connections and they seem fine.

Look in the setup screen and see if you are sending the sound to the correct place.

Consider having a shop look at it as only boards are sold for this set and guessing and installing them can get expensive.

switched HDMI plug from HDMI1 to HDMI2 port and that solved the problem

Ur backlight video inverter board is dead,need a new board.

Could be the power supply gone bad.
No easy solution I'm afraid.

42"plasma tv sound no picture

you mean no picture just sound?

lost high voltage...... check Horizontal output transitor and flyback.

I had the same problem once with my RCA television. It only happened on certain channels and didn't happen during commercial breaks. If I adjusted the volume on the tv the box went away, but came back shortly after. The problem ended up being some malfunction in the closed captioning. I turned it all off and changed the CC settings and never had the problem again.

How did the cable person hook up the cable? Was it thru an rf connector and you need to put the tv on A channel . Or are there video and audio cables from the cable box to the tv? We need to have more info please. Thanks