I have seen this issue when playing a chord from bottom up F G# A# and C when these notes are played as a chord a loud B tone sounds (instead of the C on top)…Happens in all octaves. It also happens on other notes in chords. It is almost like the chord\note sequence creates a short… I have updated firmware and also powered on with top key pressed to reset the keyboard. I see a replacement board on Syntaur but not sure if that is the fix for this…There are lots of similar posts w Reface series showing this problem. This problem does happen when controlling a module w this keyboard…any ideas outside of calling Yamaha? Thanks!
Sounds like an issue with the MK board. Probably corrosion. Order the board and rubbers