SP-500 dodgy buttons

[SteveMilner]

Greetings all!
I bought an SP-500 second hand a couple of years ago and have yet to plumb its depths. When bought, I knew the 'tempo up' button was u/s - it does nothing and is obviously visually out of place. It doesn't matter because I can use the Tap button to set speed.

I'm now trying to access the Function pages. I press the button and up comes Page 1/10. The tuning Function highlights 440Hz, and I can adjust that ...but how do I access other pages? The <PAGE> buttons don't appear to do anything. Are they u/s too, or are there other things which have to be on / off to get this to move [I'm trying to adjust MIDI settings on Function Page ]?

If buttons are not working, is it worth trying to dismantle the keyboard to access them ...give them a clean, blast of Servisol, etc.? Any suggestions welcome!
Cheers, Steve