If your printer prints like this:
This is because the developer blade for the black toner needs to be cleaned. The developer blade meters the right amount of toner that is deposited onto the drum which ultimately end up on the paper to create the image. What happens is over time, as the printer is being used, toner starts to build up a film on to the developer blade. This film get thicker and thicker reducing the amount of toner from the developer. When this occurs, the image on the paper will look faint show vertical white streaks. This can occur on any or all of the four toner developers in the imaging unit. Below describes how you can clean the developer blade.
- Open front panel.
- Remove the imaging unit by pulling green tab.
- Cover the green imaging drum with a towel.
- Remove screw from the left arm, it is located on the top left of the drum.
- Remove the waste toner tank.
- Remove screw on right side attached to the waste toner sump arm.
- Pull the sump arm to the right and upwards to dislodge it.
- Pull the left arm away from the developer section. The arm is recessed into the developer section and will require some force to unseat it.
- With both arms free, pull the drum back to separate the drum from the developers. Do this carefully, there is a spring that sits on top of the yellow developer that may fly off.
- The drum is connected to the developer assembly with some wires on the lower left side. Swing the drum to the left carefully to avoid damaging the wires.
- With the drum out of the way, side each developer cartridge out for cleaning. Don’t tip the developer cartridge hole down, since this will allow toner to spill out.
- The developers are cleaned using the same process. Remove the 5 screws that hold the plate down. Two screws hold a z shaped plates, remove them with the screws.
- When the screws are removed, lift the plate up and flip it upside down to expose the developer blade.
- The bottom side of the plate is the developer blade. It is the part of the plate that touches the developer roller. The developer blade is a thin metal strip with a 90 degree bend. It is the outside corner of this bend is where the toner builds up preventing toner to reach the image on the paper. By using a cleaning tool such as a knife or one of the z shaped plates, very very gently scrape the developer blade from one side to the other. Then change the angle that you hold your tool to get the blade edge clean. You will need several passes with your tool to ensure that the entire edge of the blade is clean of toner. You will know when you are done when the blade edge gleams and you tool will glide freely as you move back and forth down the blade.
- Reassemble the plate/developer blade back to the developer cartridge. Reinstall the middle screw and the two back screws first. There is some foam at the ends of the rollers. Using a knife or toothpick, carefully move the foam in such a way that it does not get trapped between the developer blade and the roller. Once the foam is out of the way and the blade is seated, then replace the Z plates and screws.
- Clean the other developer blades using the same process. Once all the developer cartridges are clean, reinstall the cartridges in to the developer assembly. Don’t forget to reinstall the spring on top of the yellow cartridge.
- Align the feet at the bottom of the drum to the holes on the developer assembly. Press the left arm back into it’s position on the developer assembly. This will require some force to reseat it.
- Reseat the right arm back into it position, then reinstall the screws back into the left and right arms. Reattach the waste toner tank and reinstall the imaging unit back into the printer, and close the front panel.
- Run a couple of test prints to see if the streaks are gone.
- If the streaks are still there, You could try cleaning the blades again, it could be that the blades were not cleaned enough.
- If the blades or drum are damaged in the cleaning process, then you will need to get a new imaging unit.
with the any color printing faintly down the page, then the problem is with the developer blades in the imaging unit. What happens is there are metal blades that meter the amount of toner that gets put on to the drum that makes the image on the paper. The toner is made up of fine particules of plastic. As the printer prints, some of this toner collects on the edge of the developer blades causing less and less toner to make it onto the page making the print look faint. 
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