Just found out that if you hold a C#2 chord (C#2, F2, G#2) when you turn power on and let the chord go when you see the Yamaha on the screen it goes into test mode.

You can use the data dial you run any of 39 different tests. The tests include having you press particular buttons, twirl particular knobs and move particular sliders.

We did notice that the button tests only tested one button color and did not test for blinking. So you could still have a button that wasn't 100% and might not discover the problem.