Streaks & Smears after changing toner cartridge.

Lift drum out, look down behind toner and you will see a glass lens.
Clean it with a soft cloth or tissue. Works every time.

Out of one or more toners. If you have removed and replaced a cartridge in error the % remaining is reset to 100%. Try to determine which color is missing in your print out (usually black), and then follow menu instructions to replace that cartridge. The ends are color coded so be sure you change the correct one. This will insure the remaining cartridges % remaining is correct.

using 3rd party or oem cartridge?? use Oem and or replace the image unit with a new one.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/normanj_7893313f0751935f

You can open the machine and use a pen or screwdriver to press the carousel release. Then rotate the carousel to access the cartridge to be swapped.

There are 3 things to be checked. 1: toner cartridge,try replacing it with a new on. 2: Transfer roller w/c underneath the toner cartridgelying on the printer. Removed toner cartridge,you see a roller w/c is foam like outlook,wipe it with clean dry lint free cloth or paper towel. 3: Fuser unit w/c fuse the ink on the paper.It is lacoted at the back of the machine.Remove the bottom rear cover,just by pulling it. Then you will see 2 blue color lever on left & right,turn those levers up to unlock the fuser unit,then pull out the unit. taking a look in the inner part of the unit you will see rollers . Any bad coating or damage on the roller will create smears on the prints.

What I would do is remove all cartridges, wipe the belt w/clean cloth use an air can to clean the machine, check the drum on each cartridge see if there is something, it could be there was a change in Voltage and it burnt the drums. change 1 more toner cartridge to see if that color goes away, if it does then you will know if the drums are the problems.
I've had a problem w gen toners doing the exact same thing, so I had to OEM and it went away. Good luck>

This happens to me every few months, I have to do a VERY detailed cleaning of all toner sensors. The knowledgebase on KM's website is actually very good about walking you through which sensors to clean and pictures indicating where they are located. This has fixed me up every time. GOOD LUCK!

find out where are the streaks come from, from PC drum, or transfer belt, fusin unit or from toner cartridges. does the trasferbelt and PC drum look okey. finally if nothing is helping, try firmware upgrade and replace printer drivers, sometimes help.

There are many problems like that and its not recommended to change toner from one printer to another.
but you should try: put the old toner (emty) in again, then turn off the printer, change toner and turn on printer again.
if thats not helping, then maybe you have a old FW so you can try to update the firmware.

You need to clean the printer. See your manual for instructions. It is probably dust on the laser lens