Dell 2350d/dn Mono Laser Printer - Manual (Page 142)

The printhead lens is dirty.
The toner cartridge is defective.
The fuser 2 is defective.
Try the following:
Clean the printhead lens.
Replace the toner cartridge.
Replace the fuser 2 .
Streaked horizontal lines appear on the page.
The toner cartridge may be defective, empty, or worn.
The fuser 2 may be worn or defective.
Try the following:
Replace the toner cartridge.
Replace the fuser 2 .
Streaked vertical lines appear on the page.
Toner is smeared before fusing to the paper.
The toner cartridge is defective.