I had the problem which has been described on here previously of ice forming in the bottom of the freezer section of a Samsung RL33 fridge freezer. As suggested I have removed the short rubber tube which feeds into the evaporation drip tray.
However, I noticed the coiled copper pipe which forms the evaporator has a black carbon-like coating surrounding it which has largely crumbled away (presumably due to it having been dry / hot while the drain has been blocked). There are remnants of the clear plastic tape which looked as though it was wrapped round the evaporator and its coating.
What is the function of the black coating and how important is it? I have had a few instances of the mains RCD for the house tripping recently and half suspected the fridge might be to blame as it can happen in the middle of the night when everything else is switched off.