It's common in those Panasonic CRT's. You have to adjust the screen. The screen adjust is located on the flyback transformer.
Here's a pic
Of course this should be left to a tech.... High Voltage = dangerous
Take off the cover and locate the flyback. Plug the TV and set the brightness to the middle. Get an image or signal that has black bars (16:9) or some DVD and turn the screen adjust clockwise. Make it so that the bars are not grey, but black. Try adjusting it slowly until the black becomes grey and turn it down a notch so it becomes black. All other pics should now be okay.
You can then adjust brightness(black level) in the menu for fine adjust(your liking).
If the adjust is turned too high, you will have retrace lines. Turn it down counterclockwise.
Good luck! AND DON'T TOUCH THE WIRES COMING OUT OF THE FLYBACK.