I have a Laserjet 2600n that is giving two vertical streaks of faded color on every page, whether it is B/W, color, or just a blank page run through. I can see this problematic ink on the black roller looking thing when I open the front door. I've had a similar problem with every HP I've dealt with, but haven't been able to find a solution here. I could just wipe off this ink, and see if it doesn't return, but is there anything special I need to avoid damaging anything?
Is it color specific? If so check the corresponding cartridge and see if you see the "streak" on the drum. If so replace the cartridge. If the streaks are not color specific it may be your belt. (Thats the "black roller looking thing" in the front door).
If the color streaks are on the printed side of the paper, then the belt has nothing to do with the issue since it only contacts the back of the paper. It is probably one of the toner cartridges having the issue since after or before the print job it is also leaving those same streaks on the belt before or after the paper has gone thru.