I am an owner of a PFM 500A3WU with the exact same problem.

And it wasnt dropped, just moved carefully form location ot location.

All my research tells me the panel would need to be replaced. And with sony this is VERY cost prohibitive, especially when you factor in the cost for new EDTV 42" plasma displays and the 500A3WU is a first generation plasma.

Very dissapointing especially when dealing with Sony service.

If you ever find a solution please post. But I think you and I are both out of luck and a plasma TV poorer (luckily for you yours was free)