Run a solid on each unit. One at a time and if you see lines across the solids about the size of the cylinder gears than you have worn gears. Run screeens on both units. Checks to see if you have tails or dots are not round. Again bad gears. Run a duotone on both units. Check to see if dots register correctly in the half tones. If not, bad grippers, release cams, or again gears. Also run a solid on the plate to blanket to back cylinder to look for low spots.