Canon NP6621 Service Handbook

Also see for NP6621: Service manual Service manual

3–7IMAGE FAULTS4 The copy has uneven density (darker at front).5 The copy has uneven density (lighter at front).CauseScannerPrimarychargingrollerTransferchargingassemblyPre-expo-sure lampDevelopingassemblyStep12345678ChecksClean the scanning lamp, reflectingplate, side reflecting plate, mirror,lens, and dust-proofing glass. Is theproblem corrected?Execute service mode 402 (primarycharging roller cleaning). Is theproblem corrected?Execute service mode 403 (transferroller cleaning). Is the problem cor-rected?Make several blank copies. Is theproblem corrected?Is the transfer charging roller installedsecurely?Are the position and the condition ofthe transfer charging roller pressurespring normal?Does the pre-exposure lamp remainON during copying operation?Is the developing cylinder coated witha uniform layer of toner?Yes/NoYESYESYESYESNONONONORemedyEnd.End.End.End.Install the charging rollersecurely.Correct or replace the spring.See “The pre-exposure lampfails to turn ON.”Take out the developingassembly, shake it severaltimes, and make copies. Ifthe Problem is not corrected,replace the developingassembly.