How to Troubleshoot Black Lines on Copies

By Timothy Smithee

Updated September 26, 2017

The most common cause of black lines on copies is dust on the copier glass.
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There are three possible sources of black lines on copies: the original, the scanning process and the printing process. As a general rule, if the line only appears on some documents, the source is the original. If the copier is also a printer but the lines only appear when copying, the source is the scanning. if the lines always appear, the source is a defect in printing. Since black lines can be intermittent, it is best to check all possible sources.

Check Original Size and Quality

Faint lines on the original might be more obvious on copies. Adjust contrast and brightness settings to reduce the appearance of lines. Lines at the edges of copies can be due to an original being smaller than the copy. Set the copier to enlarge the original, so the edges of the original are outside the edges of the copy, to eliminate these lines. If the original has folds, creases or pasted-on sections, ensure the original is as flat as possible.

Clean the Glass

Clean the copier glass, using a glass cleaning product. All rollers and belts should also be cleaned, and trays vacuumed, to ensure dust is not carried onto the glass. Copiers with a document feeder move the original past a small area of the document glass. As the original moves, a single speck of dust in this area will cause a line on the copy, from top to bottom. When copying, always ensure the original is completely dry, including any correction fluid and pen markings.

Clean Under the Glass

Dust can collect on the underside of the copier glass, on mirrors and on scanner elements. Cleaning this area usually requires some disassembly of the copier, and should not be done if it is under warranty or a service contract. Accessible areas should be cleaned or vacuumed. Keeping the copier in a clean non-smoking area, using good quality paper for copies, and being careful when adding toner can reduce dust buildup inside the machine.

Cleaning Toner Printers

A copier that uses toner to print has several areas where lines can be introduced, such as the transfer drum, fuser, corona wire and rollers. These are delicate and require special techniques to clean. Refer to the user manual for instructions. These components are usually easily replaced for less than the cost of a service call. Depending on the machine, these may be individual components, included in a print cartridge or included in a maintenance kit.

Cleaning Inkjet Printers

If the copier is part of an inkjet printer, ensure none of the ink cartridges are low. There is usually a software routine to clean the cartridges, and cleaning the cartridge electrical contacts can resolve printing problems. For some printers, such as those from HP, the print nozzles are part of the cartridges and cannot be cleaned. Other printers, such as Canon models, use separate print heads that can be cleaned and may need occasional replacement. Regular printing helps keep print heads clean.

Other Possible Causes

Some copiers have a collection bucket for waste toner. This should be checked and emptied regularly. Some copiers have a lever or slide-out knob to clean internal components; operate this regularly as well. Although black lines are most frequently resolved by cleaning, or replacing parts such as the transfer drum, component failure can also cause these. A partly burned-out scanner lamp, sometimes visible if copying with the lid open, will cause a thick soft-edged black line. Failure of components not included with a cartridge or maintenance kit requires professional service.