The backlight on my color display (model 06056m) does not work. If I press the button to dim, or to enter Auto Dim mode, it goes dark, and will not come on again. I have the unit plugged into a wall outlet, and also have batteries installed. It is a repeatable issue whether the batteries are installed or not. If I reset the display, the backlight will come on, but the same thing happens if I push the light button again. I have tried changing outlets, and changing the alkaline batteries. I've made sure the AC adapter is firmly inserted in the back of the unit. I purchased the device in November 2017, but just installed it 5 days ago.