Xavi, no sé la B651, pero esto del auto-dimming me ha dejado curioso y me he puesto a leer en hdtvtest.co.uk.

Y mira lo que pone de la B7000:

The auto-dimming/ black level fluctuation on the Samsung UE40B7000 can be defeated by engaging [Game Mode] and then setting [Dynamic Contrast] to “Off” (many thanks to Mr Laurent Grimal and Mr Seow who independently verified that this worked on their sets), though this solution is less than satisfactory as it entails some compromises in video processing (will be explained in a later section).
En modo GAME en la B7000 se puede desconectar al quitar "Dynamic Contrast", aunque sea una solución menos que satisfactoria porque compromete el procesamiento de video.