I've had my AP-650 for 2 months without issue. Yesterday I tried unsuccessfully to set it up in "duet" mode. I followed instructions exactly. The only sound that was generated was a very weak C note that was truncated. No other keys worked. I reset to factory default mode and same result. Is there something else I should try? Here's what I did. From fresh start up: 1) Hit music library button and lower light lit 2) Held down function button while then hitting split button and "duet off" mode on screen showed. 3) used up arrow to turn duet mode to on. Again, the only sound that would play was a weak, truncated C note. No other key played. My concern is whether any other function that I haven't tried yet is having problems?. Is there a self diagnostic test that can determine what the problem is? Will this require a service call? Otherwise the piano seems to be working normally. Thanks, Carl M.