One area to focus on is the quality of the blank Media used.
If poor quality blank Media is used can/will cause the problems your friend is having with his Duplicator. It is extremely rare instance when all Writer Drives would be defective causing writing failures but more probable that poor quality problematic blank Media the cause of the writing failures in the Writer Drivers.
Suggest to consistently obtain quality error free results only use known proven quality Media such as Taiyo Yuden or Verbatim Media that has an excellent proven track record to producing quality error free results.
As a rule of thumb DVD ROMs are better Readers than DVD Burners. As your Reading device suggest a LiteOn DVD ROM which are excellent â€˜Readersâ€™ and donâ€™t have RipLock speed restrictions.