I have an aging Alesis QS8 that has a gazillion miles on it and has earned its keep many times over. Recently at live gigs I (and other band members) had noticed some distortion from the keyboard. I listened with headphones and heard it there also. I played it for a local repair tech and while he couldn't notice the distortion, he suggested it might be more prudent to just buy another board (not from him) as global type distortion could just be that the board is wearing out. I wonder if any other Alesis users have had this happen? I ordered a new QS8.2 anyway so I'll keep or sell the old faithful board. I really love the feel and sound of the Alesis and up until recently have considered it bullet proof. I guess we're all getting older.
Regards,
Pat

the output DAC may need replacing, or an opamp may be gone. also check power supply voltages to see that they haven't wandered off course.