Mita DC 1860 3 dark horizontal streaks

The black lines you have sound like a bad drum cleaning blade. If you want to take out the drum unit, first you have to remove the two black screws that hold the process unit in. You can find these inside the front door of machine, you will see a metal plate that is attached to the toner hopper, the black screws are in the upper left & the upper right of that plate. You can then slide out the process unit, it should stop about half way out. Lift up on the orange handle and slide it the rest of the way out. If you have to clean the drum use a soft dry cloth first, pull the drum shaft out and the drum will lift out, if the lines do not go away you can use alcohol & then wipe off as much residew as possiable. If the black lines return after reasembly you have a bad cleaning blade. Hope this helps, Let me know if you need more help.