To test beam - Open freezer door and hold the flapper down on the left hand board.(make sure your hand doesnt block the beam) the red light on the right hand board should remain lit. There should be a "tech sheet" in the toe grill of your fridge that explains all the blinking patterns. If the ice maker is in a harvest cycle it will blink in a certain way. Now saying all this.... the beam boards amy still be defective even with a solid light. Some part suppliers call it the "optic board" (you get the emmiter and receiver boards in one kit)
Whirlpool also has a bulletin on these "in door ice" models where the water supply line to the icemaker freezes up. There is a kit with new water line and heater to prevent line from freezing