Observing a few rules of thumb can help you quickly isolate the source of many copy quality defects produced by a copier. First, begin by making enlarged and reduced copies and note whether or not the defect also changes size. If it does, the problem will most likely be found in the optical section of the copier. Vertical lines running from leading to trailing edges commonly result from optics contamination. Second, white horizontal bands or blurriness on copies typically indicate a scanner malfunction, whereas black horizontal bands indicate "jitter" in the drum drive/paper transport mechanisms. Third, if the defect repeats more than once on a single copy, roll the paper into a cylinder so that the multiple occurrences of the defect line up; then note the size of this paper cylinder. The machine problem will most likely be found on or near a component of approximately the same diameter (e.g., the drum, magnetic cylinder, fuser roller, etc.).