Whole row of buttons not working..

Currently have an MPC3000 and the 0/./Enter/Tempo Sync/Transpose/Simul Seq row of buttons are non operational.

I opened it up and there's continuity on all 6 buttons when pressed, so it's not the contacts (would be pretty unusual for all 6 to go like that anyway)

I checked the service manual and traced all 6 buttons to a diode d615. I tested the diode with my multimeter (with help from google) but its fine too.

any ideas would be really appreciated! everything else works flawlessly on it, it would be amazing to get it up and running as it's been in someones loft for 10 years!

Verify all your ribbon cables are securely connected to the circuit boards.
If those are all good, check for cracks in the circuit board traces near the tact switch buttons.

If the continuity between the Simul Seq switch and diode D615 is ok, then I bet IC 604 has failed - it's a 74HC138, for some reason these are not very reliable, I always seem to be replacing them in old gear.