I'm really surprised, that nobody knows the problem of the white screen.
I have 16:9 units for X5 and also for E38/E39. They are different. The monitor part has a different part no. and the casette unit has also different part no. in case of E39 and X5.
E39
monitor: 65 52 6 934 415 (old partno.:65 52 6 913 385)
unit: 65 52 6 928 389
X5
monitor: 65 52 6 934 416 (old partno.:65 52 6 915 517)
unit:65 52 6 988 771

If you mix the units (eg. E39 unit with X5 monitor), you will get white screen. I don't know the exact reason, but I had the white screen problem 2 times, and both were because of mixing the units.
Check the part numbers. The monitor's parts number is on the back side, so you have to push the eject button to check it.

Bombolo