Freezer not defrosting, new main board installed.
You will want to pull the door and shelving out of the freezer compartment and remove the rear cover of the freezer. Once the rear cover in the freezer has been removed you will want to do a continuity test on the defrost thermostat and the defrost heater. If one of these does not have continuity then replace the part. Since the new control board has been installed then one of these 2 parts would be the issue.