... Now, the only thing that doesn't works is the E5 key tha plays only

> the maximum thelocity also if you press very soft.
> I don't know how resolve the problem.
> Anyone had the same problem?

Following but to Ben's note, each key on the Polaris actually has two
contact pads under it. When should make contact towards the top of the
key-press, while the other should make contact towards the bottom of the
key-press.

The keyboard will look at the time between those two presses and use that
information to try to calculate velocity.

The contacts are implemented via a rubber neck, which has a conductive patch
on the other side. If that neck is bent, or if there's dirt preventing the
proper operation, then odd results may occur.

If you pull out the key itself, you should be able to see these contacts.
You can press on them/wiggle them with your finger tip and make sure they're
making contact as expected. Of course, if you can get in to them - cleaning
the contacts themselves is always a good idea.

One other (less likely) posibility is the software setup on the Polaris.
There is a process noted in the service manual which allow you to
individually adjust the sensitivity of individual keys.