Im not quite sure what you mean by a bad panel display and what causes it.
The plasma panal is made up of a bunch of IC's that process the picture information
Each IC's takes care of a certain area of the plasama display
these IC's are mounted on FILM ribbon cable and are not replaceable once they go bad
The Ic that processes the area of the pix youare ahaving issue with has failed
what causes it?
Excessive Heat over the years chiping away at he glue/solder that was used to mount the ic to the cable
it cant be repaired once this happens