I was thinking of improving YDS octave switch function/sensitivity as orginal octave switch can be inaccurate or sluggish when fast ocatve change is needed. First I was looking for guidance on how to dissemble YDS-150/120. I found one at youtube.
Here is my final modification of the octave keys- more accurate and faster octave changes. Without moving the thumb widely, I can change octave up and down easily and instantly.
After testing for a while, this is my my final modification. I am very happy with this.