A13-LCD43TS brightness

[ulink]

My A13-LCD43TS ist not very bright, far away from the 400cd/m2 stated in the data sheet (I know that the touch panel absorbses some light but can't be that much).

Scope shows that even at 100% pwm duty the TFT LED voltage is only 20V, datasheet and switching regulator schematic says this should be 28V.

Whats wrong here?

[ulink]

Recently tested the brightness of the two 4.3 TFT with touch versions:

New LCD-OLinuXino-4.3TS: 174lx
Old A13-LCD43TS        :  70lx