I seem to have a failure of the defrost controller. This happened once before, about 10 years ago, and the symptoms are similar: back of the freezer is all iced up, but temperature is high in refrigerator and freezer. I have ordered the controller board (still have the old, dead one right here).

While waiting, I defrosted by hand, thinking this would put me in good shape for a few days at least. But it didn't. After about 12 hours quite a bit of snow and ice had built up again, but the overall freezer temp was too high to freeze any liquid. Refrigerator temp was high too, around 60F.

Is something else wrong besides the defrost cycle? How could the evaporator be cold enough to form all that snow and ice, yet not get the rest of the box cold?

Also, what makes these defrost control boards go bad, and is there any chance of repair? The board isn't complicated: all through-hole components, only one IC (a PIC16 microcontroller), two transistors, some resistors, capacitors and diodes, and a big relay switch. There are no signs of injury or damage to anything on the board. I would guess the relay, having nothing else to go on. Advice?