Luis,

Andrea is right : The SD1 has no 'warranty seals'....
I would open the SD1 right away (because of my profession) but if you are not familiar with delicate electronic equipment you'd better not ! (Many things can go wrong)

The pitch-wheel in most keyboards have 2 springs (one for each direction) It looks like the 'center' mechanism is broken or out of position.
Do both directions still have a 'spring-feel' ? ..... If not, one of them could possibly be traveling in the SD1 (and can cause major damage to the electronic parts.

Fortunately I have not seen the internals of my SD1

Roel