upper Caceの開け方は、このように記載がありますね。
底面ワッシャー付き3個、
バックパネル7+3+1+2+1= 計14個を外す様ですねね。再検討してみます
1. To open the upper case
A stick of wood is required to hold the top panel open. Get one first!
1.1 On the bottom panel, remove (3) 4x18 screws labeled "E".
↑これはたぶん大きいワッシャー付きの3個と思われる。
1.2 On the back panel, remove
(7) screws, all near the card slots and MIDI jacks.
(3) screws near the card slots (one each side, one under);
(1) screw between card slots and MIDI jacks;
(2) screws, one each side of the MIDI jacks;
(1) screw closest to MIDI jack screw.
1.3 Open the upper case being CAREFUL not to touch the card slot on the rear panel and both side plates.
You should now be able to change the battery or do other simple repairs.