I had a customer with a 750C with a history of spc, C021 and CE40 codes. They fixed the C021 code by replacing the dv,mix motors. It worked for a couple of months. I fixed the CE40 code but afterwards no color what so ever. I found out it was a gear in the dv drive assymbly that had broken some teeth. The part # for the gear is line # 19 // 305JN711MO