Black Lines On Colour Prints

[posterboy]

I just bought a Refurbished HP 5550dn Colour Printer, I printed off some sample prints, and I see that there are light horizontal black lines, regular intervals, they can only been seen when printing off colour prints.The lines only appear at the middle and lower part of the print, the top is fine. Im not sure what to do, or how much it would cost to fix.

 

[posterboy]

there are three main black lines, the distance between the lines are aprox 2 inches apart