Brother MFC-8420 User Manual page 394

Examples of poor print
quality
Curl or wave
B DEFGH
abc efghijk
A C D
b c d e
1 3 4
Wrinkles or creases
The drum unit is a consumable item and it is necessary to
replace it periodically.
TROUBLESHOOTING AND ROUTINE MAINTENANCE 22 - 20
Recommendation
Check the paper type and quality. High temperatures and high humidity
will cause paper to curl.
If you don't use the printer very often, the paper may have been in the
paper tray too long. Turn over the stack of paper in the paper tray. Also,
try fanning the paper stack and then rotating the paper 180° in the paper
tray.
Try printing using the straight-through output path. (See How to load
paper on page 2-5.)
Make sure that paper is loaded properly.
Check the paper type and quality. (See About paper on page 2-1.)
Try printing using the straight-through output path. (See How to load
paper on page 2-5.)
Turn over the stack of paper in the tray or try rotating the paper 180° in
the input tray.