HP 16V - Manual (Page 126)

Print Quality Problems
Print Quality
Problems
The most common cause of poor print quality is the dirty corona
wire or precharger wire. A rare cause is the expired fuser unit. The
figures below show the typical appearances.
Due to dirty corona wire
Too light White vertical line Ghost printing
IF
Due to dirty precharger wire
Black vertical line Due to both
Toner stains (back) Smudging
F
Due to expired fuser unit
Blurred black vertical line
User’s Manual 5-11