Delonghi Magnifica S grinding time too short (3 seconds)

I have a Magnifica S, ECAM 22.110 B, but the grinding time is too short. I've heard that at maximum value, should grind about 7-8 seconds. Mine always grinds for 3 seconds no matter of the location of the dial (the frontal chromed dial with coffee beans drawn on it). I've tried to reset the encoder, but this seems only to work for one shot. I've seen the frontal board and seems ok. I am not sure if there is a problem in another place. The grinder has been cleaned and the grinding size as well. The only thing that does not work is grinding for more than 3 seconds at maximum dial settings and continuously in every serving.

If anyone has technical documents of the machine, the boards of the machine, schematics, etc., like the ones that use the technical service, I would appreciate if it can be sent to me or attached for download.

Thank you very much in advance for your help.

Regards,

David.