99.9% to be a fault on the plasma panel - one of the column driver chips has bust or come away from its tab bonding. Nothing to do with the HomeHub!
It needs a replacement panel, go back to where he bought it (if still in warranty) or contact Panasonic as they generally have very good warranties (normally one of the more reliable makers). If it is out of warranty (sellers or Panasonic) then a repair (replacing panel) will be as expensive as buying a new one, I'm afraid.