GE side by side fridge still not defrosting

My GE fridge freezer is still not defrosting. I have changed the defrost thermostat and the defrost heater. Not sure where to go with it next. I saw on the repair clinic help section that the main control board is the next option. There are two on there, one is $41 and the other $149. I am wondering which one to try first and also if there is a way of finding out that they are bad. Any help or suggestions would be greatly appreciated.

Thank You very much
Don