Good afternoon. I am flying the 777 from ORD to LAX after pressing the TERR button to ensure I had it working. When I turned the knob for both the TERR and WX brightness on the ND it didn't work. The displays would also not DIM. the only thing I see happening is that when I twist the small knob the TERR refresh gets reset and it kind of flickers on the ND. Neither do the PFD nor the ND dim switch are responding. They stay at the same brightness no matter what I do with the brightness knobs. 

Turn off the Master Brightness on the overhead panel and then control the individual screens with the associated brightness knob. You push the button in the middle of the Master Bright dial to do this.