I have a radio installation with two KX-155 Nav-Comms. These radios are equipped with a photocell to automatically dim the displays to match cabin lighting. In dark lighting, the digits fade to the point of unreadability, with some segments being visible and some not. I can brighten and read the displays by aiming a flashlight into the photocells.
It seems like there is a bias set incorrectly or an excitation voltage which is wrong.
Why might this be happening?