The present invention provides a cabin pressure control system that comprises a first outflow valve having a first motor controlled by a first outflow valve controller, the first outflow valve having a first backup motor controlled by a first backup controller. In one example, the method includes receiving test data that represents an attribute of a tested electrical device. Each of the plurality of voltage drop setup circuits includes a resistor parallelly coupled to the switch. The masking layers together form a step opening structure that exposes the under-ball-metallic layer. A refrigerator according to an aspect includes: a freezing compartment; a freezing compartment door; an ice bin mounted on the rear of the freezing compartment door and storing ice; and an operating unit mounted on the rear of the freezing compartment door and operates to discharge the ice from the ice bin.