MFC-8420 FAQs & Troubleshooting MFC-8420 Not your product? Sort by: Updated Date Popularity 2 Results 1. 17/09/2014 Why are my sent faxes always received with a black vertical line down the page? 2. 27/08/2014 How do I improve the copy or fax quality? More FAQs Fax FAQs & Troubleshooting