that panel was very loosely hinged and rested back just by gravity alone. If you let go while closing just past the vertical it would fall with a crash. The 6100 was metal, by the 6300 it had turned into plastic.
I rememeber the music stand as folding into the top edge of the panel and being very flimsy indeed!
Ah! memories, those machines were so cool in their day, now they must sound awful. They were my first 'serious' keyboards