Repair of Store Digital 7DVD writer

We have a Store Digital 7 DVD copier that is in need of repair. details are as follows: S/N: 004476 Fault: It wouldn\'t detect the size of the disc and put 448 MB whatever disc was in there and whilst duplicating the discs it would fail about halfway through. Also every 4th batch would fail and the machine would require a restart. Sometimes 1 disc would fail - no specific tray... Although originally purchased from you guys, we don\'t seem to be able to track down the invoice number.