Was your display intermittent when you changed the bulbs? Mine is intermittent, but in the right light conditions I can see that the unit is functional, just not illuminated. My buttons are backlit, just the actual display is not lit up (it does however tend to come on randomly every once in a great while). Does this indicate bad bulbs? Seems to me more like maybe a loose wire or bad ground. Are there any common points to check? Anyone else come up with a different solution to an intermittent issue?
