MFC-7840W FAQs & Troubleshooting MFC-7840W Not your product? Sort by: Updated Date Popularity 3 Results 1. 16/12/2014 How do I make my faxed documents lighter or darker? (Fax Contrast) 2. 15/05/2013 How do I clean white or black spots on printed documents? 3. 14/01/2008 Why are the faxes I send always received with a black vertical line down the page? Fax FAQs & Troubleshooting