I got assigned a printer call on this device. Previous to my arrival someone had replaced a maintenance kit, it included:
Fuser Transfer roller Charge Roller Pick up roller Toner cart
I went there found the toner cartridge had a strip of film missing from the cartridge, I replaced with a toner cartridge that was previously in there, cleaned up the printer (toner was in the trays and on the pickup rollers). Issue was resolve for the rest of the day.
Today I am called and it has returned, I ave not seen it yet, but am curious as to what else to check? Any ideas?
More aboutlexmark t642 vertical lines toner
Lines may be caused by toner build-up on the corona wire. There's usually a special brush for that in the toner kit or a fixed brush that slides across. If stuck I'd download the manual for the printer from the Lexmark support site.