Dell 5110cn black toner

you should adjust the toners

Sounds like a bad toner, or possibly the scanner is dirty. If you look where it pulls the paper through it can have a small speck, but since its on the scanner tself it will put black lines all the way down the paper.
If its larger and smeared the Toner itself is probably bad and you need a new Toner Kit, should come with new rollers and a new cartridge as well.

If there is black "dust" all over the developer (behind the image drum assembly ) you need to replace the developer; that is uncoated toner prevenitng transference of colored toner.

try to print test page and determinate which or colour is fainting. if it is one colour then you need to replace this colour image drum. If all of colors is fainting then its transfer roller.

try to print test pages, check if toner is fused to paper. probobly toner issues

Without seeing the lines but you said they are colored I would guess the color pcu needs to be replaced.

did you check the drum? drum might be bad

I GOT A CLARIFICATION REQUEST AND I SENT FURTHER INFORMATION BUT AS OF YET I HAVE NOT RECIEVED ANY FURTHER INFORMATION BACK FROM "KEEPITSIMPLE".

Good Evening Robert,

The setting for non dell toner only controls the fuser temperature, and will not cause you any print quality issues. Toner is actually made up of ink and plastic. The fuser melts the plastic to "fuse" the image to the paper. Dell toner is set to "fuse" at a specific temperature. when you use non Dell toners, the temperature required to fuse may be different, and when set to non dell toner setting, the fuser temperature is raised to the maximum to ensure the other toner fuses properly. The down side to this is that you will wear out the fuser sooner then it should.

As far as the print quality issue you are having, it is most likey caused by the imaging drum.

Regardless of the estimated life for the imaging drum as stated by the printer, this is just an estimate. Many things can and will cause the imaging drum need replacing. ( Just yesterday I replaced a black toner in a 3115 that was less then a month old... genuine Dell... with more then 75% expected usage left because it was defective).

On this printer, each of the 3 colors and the black are all independent of each other with the exception of the imaging drum. Even within the imaging drum, cyan and black are independent of magenta and yellow on the first stage of transfer. When you have deteriorated print quality that effects more then one color, the first step is to replace the imaging drum.

The Primary transfer, secondary transfer, and tertiary transfer of the image are ALL contained within the imaging drum.

The chances of having 3 or 4 bad Developers is very very slim. If your print quality issue was related to only ONE color, then I would say you had a bad developer unit ( the 4 items located behind the imaging drum when removed). These are far more difficult and expensive to change.

The BTR ( bios transfer roller ) is the only other item that "could" effect your print quality, however, based on the symptoms you discribed, I doubt it. Besides, if i am not mistaken, the imaging drum kit comes with a new btr anyway.

Although I am sure you may be disappointed with the fact the drum unit is failing while showing it still has life remaining, the solution to replace it should restore your unit to full operation. The unit is light sensative, and effected by physical age as well as the number of prints it has supplied.

Please evaluate the solution i have provided and, rate the solution appropriately to show your support.

Thanks,
Cory

Have you tried doing a recalibration cycle ? Had trouble here following installing a new blue toner. Everything was TOO intense. Tried turning power on and off a few times and then finally found the route to forcing a full re-calibration.  Ready -->Menu select -->Menu Engine --> >Engine service -->Color calibration. 
Now if we could just get rid of these lousy streaks on the side  =<