Casio ctk 620l keys faulty

I have a ctk 620 casio keyboard, when you press one key u will here 5notes sounding at once please anyone has an idea what could cause it am very sure it is not from d key contact I checked it is perfectly clean from water or rust

Are you getting the multiple notes no matter which note you play? Or does it happen when you play one particular key?

Thanks Sam
I don’t get that fault when I press key it only happens on 3 of d F# and Bb flat keys when I press one of d F#, 5notes will sound together.

We don’t have any service info for that keyboard, so I don’t have anything to refer to. Did this just suddenly start happening, or did it start after the keybed had been worked on? Do the rubber contact strips mostly span one octave each, or is there a single strip across the entire keybed?