[GreenKeys] Newbie seeking help please

[E.]

So many people have helped me out greatly on this list when I first got started… I will always be in their debt.  I have a couple/few 15/19’s here and there (along with a couple of 28s).  My one piece of advice is to do your research before doing much of anything and check & double check before attempting anything because if something breaks, it’s kind’a somewhat pretty hard to close to impossible to find replacement parts anymore… so take it nice and slow and you should be fine :) .  Ah, also - don’t forget to oil.  Beautiful machine - so clean on the inside ;D !

Looking at the keyboard - what is that knob on the lower-left part of the upper part of the keyboard unit?... clear as day, right ;p ?