Mark 12i problems

[Steven Kennedy]

Hi everyone. I am really stuck with this one. So I have a Mark 12i and here is the rundown of whats happening. D4 plays a repeated note when pressed (but plays Bb4), Bb4 repeats (but plays F#5), F#5 repeats ( but plays D6) D6 repeats (but plays Bb6), Bb6 repeats (but plays F#7), F#7 is a dead key. And yes they all are 8 keys away from one another. Any idea? I don't mind digging in to the keyboard, I'm just a bit lost as to where to start. Thanks in advance.