The DF models were not fitted with the same batch of defective image sensors that plagued a very large number of "D" models (this according to JVC anyway!) their breaking down resulting in the infamous "lens cap on" problem which attracted a free repair. (list published showing range qualifying for repair) However the other point is that on the DF ranges the lens assembly itself was a suspect area as the cause of the problem, and in many cases it was changed to alleviate the fault, so there isn't one definite thing that could be pinned as responsible. To be honest there isn't anything that can be done outside of a test bench environment with the equipment necessary at hand to carry out testing.