Samsung CLP 325 colour laser printer fault

I have a Samsung CLP 325 laser colour printer, some years' old. It prints perfectly in black only. In fact, I have just bought three toner cartridges, one of which was 'K' (black) and the mono printout is really excellent. When I print in colour, however, the following happens (1) a second image of the print-out appears on the page and (2) the printer throws coloured toner (mainly cyan and magenta) all over the page, creating a dirty background and vertical streaks. It seems so puzzling. What is wrong? Tom Sharp

Question by Thomas Sharp on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.