Using my Roland Rd300s Digital Piano as midi keyboard for writing. When you turn it on it defaults to two-channel MIDI transmission, which is no good for writing notation, as it duplicates all notes ... you write a 'c' and you get two 'c's. I got the keyboard 2nd hand, so I never had an instruction manual, and it's quite old now. Until today, I found by experimentation that I could switch off one of the channels by pressing the button on the left of the picture below in combination with either of the two lit buttons marked 'L and 'U' and then one would switch off. But now whatever I do, both channels seem to be permanently 'on'. Have I forgotten the right button combination? Has a switch stopped working? Are there any Roland RD300 users (or sound engineer types) , who can tell me where I am going wrong, and how I can fix it. It's not worth spending much money, given the age and condition, so I'm hoping for a DIY fix. Thank you!