I have to say that's one feature I really liked about Yamaha arrangers. When I had my PSR-550 I had all the test codes for it. It was fun checking all that stuff out. There was one test I always played with to freak out my wife. You could run a test and turn on EVERY LED light on the panel. My 550 lit up like a Christmas tree with that test.

Squeak
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.