Our Brother Intellifax 3800 when it's making large black lines on the paper?

this sounds like a reasonabley common laser-printer-type problem.

I suspect it could be your drum unit that's worn out or damaged in one or more places - this can happen by physical trauma, or by over-exposure to light. These look expensive to replace, you might try to get one under warranty.

The problem may not be the drum & it's free to try this solution:
You should give the machine a good clean: you'll need to take the machine apart: toner cart, front panel etc - things that are easily removeable - I'm not talking about using a screwdriver (or hammer :)

then attack it with a hoover.

Chris Murphy
September 2006