Luis,
the SD1 case is not sealed, so you can try to open it carefully. You have to unscrew all the big screws on the sides and the small ones on the rear end, plus a few ones. Do not unscrew the big screws in the middle because they secure the keybed. Then you can try as AJ suggested: reverse the spring and see what happens.
Good luck.
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.