85% of paper jams are caused by worn rollers . The rubber treads in the rollers wears down, making them smooth, so they won't pick up the paper. Sometimes, they are aged, which also gives them a smoother rounded texture, causing jams. The quick fix is to liven up that roller with a mixture of alcohol and soap. Damp a rag with the solution and wipe the rollers clean with it. That's make them more pliable and the paper jams will cease.
Here is the manual, see chapter 11, page 11-7
http://www.vikingdirect.co.uk/speciallinks/gb/vkg/source/MFC7420_7820N.pdf
Click on this link or copy and paste the complete link into your browser.
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Thanks, Joe
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