In this case you really need a tech. It could be from the black LPH (Led Print Head), or (worst) from the ESS PWB (main board of the machine).
Sorry to hear that... that's unfortunate (and surprising).
I personally can't think of anything else to try. But if I do think of something, I will post again.
It could be a problem from black drum cartridge (posiible discharge as per Andy indication), because from your image there is no image interruption on color mode (on lower of the page, cyan/blue text).