DIAGNOSIS Streaks with a new cartridge usually mean the transfer roller or the fuser unit is dirty or worn. Toner is sticking to a dirty surface inside the printer and getting smeared onto the page.
FIX First, run the printer's internal cleaning cycle. On the control panel, press the 'Settings' button (the wrench icon). Navigate to 'Maintenance' and then select 'Clean Drum'. The printer will run for a minute or two. Print a test page (like the printer configuration page from the network menu) to see if the streaks are gone.
IF THAT DIDN'T WORK The issue is likely the transfer roller, which is a long rubber roller you can access by opening the front cover and looking beneath where the toner cartridge sits. Power off and unplug the printer. Use a dry, lint-free cloth to gently wipe the entire length of the black transfer roller to remove any built-up toner dust.
HEADS UP If the streaks are repeating at precise intervals (like every 2 inches), it's a defect on the drum of the toner cartridge itself. Even new cartridges can be faulty. If cleaning doesn't work, you might need to exchange the TN-660 cartridge.