My 5 yr old Samsung RS267 refrigerator is not holding temp. It is just out of warranty. There was ice buildup on the evaporator. The heater measured open at the main PCB. Replaced the heater. You can see where the old one burnt open. The new one measures 48 ohms at the main board but I am still getting ice buildup and temperature fluctuation. The self-diagnostic LED 07 shows a REFRIGERATOR DEFROST HEATER error ("in the refrigerator room, if frost removal mode is finished due to limited time of 80 minutes. Error is displayed") The Freezer is fine. The frig also has a new fan and it is running OK. Any idea what to check next. I am thinking of changing the main PCB.