Rhodes Chroma Polaris

Hello everyone. I am looking to buy a Polaris, I went over to the
owners house and checked out the synth. All the membrane switches
appear to be functioning, with the exception of the master tune button
(the one in the third column from the left). In the manual it said
that the lights would only light up for each voice that was being
tuned, correct? So if the synth is in tune, does the button light up
when it is depressed, or only if it is out of tune? No matter what
other buttons were pressed in combination with it, it would not light
up. Is it broken? The synth itself sounded like it was tuned at the time. 

Also, can this function be accessed through an external midi control?
Or does the synth require a repair.

Thanks so much