Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
That sort of problem can only be caused by one thing:
- a defect in the yellow toner cartridge.
Whether it is the 'bottle' kind (in which case it is leaking badly in all likelihood), or the toner-and-drum type (in which case several things may be wrong with it), it needs to be re-seated at least (and toner leakage checked for!) and probably replaced. (I'd say replace it, unless it simply slipped loose of its mountings and is the bottle type and just re-securing it in place will cure the problem ... provided that it does not slip loose again.)
With symptoms like this, I really have little doubt that this is the problem, and the solution, essentially. In case there might be more to it, be assured, I stand ready to help and advise you further if there are other details I might not have guessed at.
Let me know how it goes, please.