A common problem that I run into with HP Color LaserJet 3500, 3550, 3700 printers is toner specks running down the paper vertically. This problem is different than periodic dots that show up on the page at defined intervals, otherwise known as repetitive defects. With a repetitive defect, note the color of the dot and measure the distance between the dots. The service manual describes what internal roller is causing the problem and you can simply replace the appropriate part.
Random toner specks can be a little more difficult to diagnose. Continue reading