Hi, I'm encountering a really strange behavior with a WC 3220. When it prints only one side everything is ok and the printout is perfect. But when I try duplex copying or printing something strange happens. As you can see from the attached document side 2 (the first page of the file) comes out ok but side 1 shows those black horizontal lines and doesn't print correctly. I don't understand which part of the machine could cause this problem. I tried a new original cartridge with same result. Also changed HVPS but no success. What other parts could be involved and have you ever seen this?

Thank you
WORKCENTRE 3220.pdf