Editing Laser printing (section)

===Malfunctions===
The mechanism inside a laser printer is somewhat delicate and, once damaged, often impossible to repair.  The drum, in particular, is a critical component: it must not be left exposed to ambient light for more than a few hours, as light is what causes it to lose its charge and will eventually wear it out.  Anything that interferes with the operation of the laser such as a scrap of torn paper may prevent the laser from discharging some portion of the drum, causing those areas to appear as white vertical streaks.  If the neutral wiper blade fails to remove residual toner from the drum's surface, that toner may circulate on the drum a second time, causing smears on the printed page with each revolution.  If the charge roller becomes damaged or does not have enough power, it may fail to adequately negatively charge the surface of the drum, allowing the drum to pick up excessive toner on the next revolution from the developer roll and causing a repeated but fainter image from the previous revolution to appear down the page.

If the toner doctor blade does not ensure that a smooth, even layer of toner is applied to the developer roll, the resulting printout may have white streaks from this in places where the blade has scraped off too much toner. Alternatively, if the blade allows too much toner to remain on the developer roll, the toner particles might come loose as the roll turns, precipitate onto the paper below, and become bonded to the paper during the fusing process. This will result in a general darkening of the printed page in broad vertical stripes with very soft edges.

If the fuser roller does not reach a high enough temperature or if the ambient humidity is too high, the toner will not fuse well to the paper and may flake off after printing.  If the fuser is too hot, the plastic component of the toner may smear, causing the printed text to look like it is wet or smudged, or may cause the melted toner to soak through the paper to the backside.

Different manufacturers claim that their toners are specifically developed for their printers and that other toner formulations may not match the original specifications in terms of either tendency to accept a negative charge, to move to the discharged areas of the photoreceptor drum from the developer roll, to fuse appropriately to the paper, or to come off the drum cleanly in each revolution.{{citation needed|date=February 2016}}