How do I make Vocal Harmony function on s970?
I've read both Owners and Reference Manuals with no success. Unlike s910 you just press the Harmony button and you are good to go!
It's not correct that "you just press the Harmony button" on any Yamaha keyboard, 910 or otherwise.
The Harmony button, on all Yamaha keyboards, triggers harmony chords in the right hand. To trigger vocal harmony, you need to press the Vocal Harmony button.
So perhaps this is your problem. You just need to find the Vocal Harmony button.