MFC-7840W FAQs & Troubleshooting MFC-7840W Not your product? Sort by: Updated Date Popularity 4 Results 1. 11/03/2016 How do I clean the corona wire? 2. 21/11/2012 How do I clean the drum unit? 3. 06/03/2008 How do I clean the laser scanner window? 4. 24/01/2008 How do I clean the scanner to improve the copy or fax quality? More FAQs Cleaning FAQs & Troubleshooting