Dave,
When in any fingered chord mode, if you play 3 lefthand notes together (for example F, F#, G) then all the arranger parts except the drums stop. When you play at least a 3-note chord, the other parts resume. It's a very useful function that you probably already know about.
I know this function is also on 740, 640, 540, 8000, etc.
DonM