You have to loosen all the big black screws on the sides and on the back of the keyboard, plus some small ones. Don't lose the big screws which go in parallel (two at a time) along the middle of the keyboard because they just secure the keybed.
You have to experiment a bit.
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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.