Samsung ps50a556 Grainy picture ... gets worse until shutdown.

[clark97]

Samsung 50" HD Plasma PS 50a556 when switched on has a slightly grainy picture which gets worse as the set warms up until you end up with whats in the photo :

Any help greatly appreciated. Looks z sus related as once like this it takes ages for image to appear and leaves a temporary image burn.

Thanks in advance guys.