Brother HL-3400CN Series - Manual (Page 188)

CHAPTER 5 MAINTENANCE
5-31
Periodic Printer Cleaning
Every 20,000 pages printed or every 12 months, we recommend cleaning the
following parts with a dry cloth.
Clean the Paper Guide and Registration Roller to prevent paper jams.
Fig. 5-35 Paper Guide and Registration Roller
Clean the Exit Roller after opening the Top Cover slightly. This will help
to prevent paper jams at the paper exit or dirt from appearing on your
print output.
Fig. 5-36 Top cover and Exit Roller