Hello, The
Kyocera FS-4000 have a
separate Drum Unit and Developer unit installed.
The Developer delivers the toner to the drum unit, either could cause the issue you are describing. The
Fuser in the back is also a
possibility, however remote for this discussion. The most likely component failing is the developer unit. The developer is
accessed by flipping the top cover and withdrawing the developer out. Look at the developer roller for a smudge or smear, you may be able to smooth out any smudges with a piece of paper, do NOT use your hands or any liquid of any kind. The drum unit slides out the left side of the
printer VIA the access panel. The cost of these components can be quite a bit. If you have any spare I would install them one at a time and see if you can determine which is causing the problem.
302F993011 DK-310 (Drum Unit)
302F993030 DV-322U (Developer Unit)
302F993072 FK-320U (Fuser Unit)