I am a user of a Yamaha Modx6 and today when turning on the keyboard, the keyboard sound was distorted. I realized that this is only occurring when there is an inserted effect. I downgraded and updated the Modx system and the problem persisted. I did the system tests and a failure was detected in "Ic 803" and "Ic 804". The keyboard never suffered any kind of accident, I don't know what to do.
I got in touch with Yamaha Brasil and they didn't even answer my email.