NAV screen is dim now no matter what I do

[X5only]

Hi,

The NAV screen on my '05 4.4 sports has gone dim for the second time now and no matter what I do this time around, it hasn't gone back to the usual brightness it has had. The first time it dimmed (about a month ago) I drove the car hard and it brightened up next time the car was started- it may have been a fluke. Now I've done the same, updated the NAV OS to the latest (v32), ensured the brightness settings are on the highest level, the instrument cluster dimmer knob is on brightest setting - all to avail. The color scheme is on 1 but even on 2 it's still dim.

I was suspecting the battery (still original) but no starting problems or other lighting problems so I figured it can't be the battery. Is there a bulb in there that may need to be replaced? Has anyone experienced such a weird issue?

05 X5 4.4 sports 62K miles.