Toner may transfer to the roller surface following a paper jam or if the paper is smaller than the image. Periodic cleaning of the roller is required to prevent this toner from migrating back to the rear of new printouts.
The machine cleans the roller at the following times:
- After initial power on.
- After clearing of a copy jam
- At the end of a job
The PSU first supplies a negative cleaning current (about -4 A) to the transfer roller, causing negatively charged toner on the roller to move back to the drum. It then applies a positive cleaning current (+5 A) to the roller, causing any positively charged toner to migrate back to the drum.