He said C#0, A0, F1, C#1, A2, F3, C#4, G4, A4, A#4, which would be every 8 notes, except for the G4 and A#4. The G4 and A#4 may just be bad contacts. The others (any C#, A, F) is every eighth note and could indicate a bad wire to the keyboard, or a bad trace or diode on the matrix circuit board under the keys where the contacts are, or a problem on the KLM-366 between the keyboard connector (CN04) and the chips it connects to, or a problem on one of those chips. That is quite a few possibilities. I guess the real clues would be the fact that the arpeggiator does recognize that the key has been pressed even though it makes no sound when the arpeggiator is not engaged, and the strange statement that there is a “hanging note” when using Chord Memory. More details are needed on that. For the wiring to the keyboard, you would need to carefully inspect a disassembled key contact board to see which wire in the matrix is connected to all C#, A and F keys.