The defrost control board is at the back right hand side of the control housing. The housing has to be dropped down to access the defrost board.
The white plastic enclosure around the board separates into a top and bottom.You will see where the wires plug into the board. With the power on,
take a phillips screwdriver and short the first and second pin on the left side. The refrigerator needs to be running when you do this. You should hear a click and the fans and compressor should shut off. Usually nothing happens which means the control board is bad.