Like most mechanical devices, laser printers sometimes fail to work or produce unexpected or inconsistent results. Each model of laser printer is different, and may develop different faults. The following chapter describes some of the problems which occur on laser printers, and the likely sources of such problems. The advice given in this chapter is not a substitute for the troubleshooting section in a laser printer user manual, but it may give some insight about why a particular problem occurs. Read the cautions below before attempting to correct any problem, and always read and obey the cautions and procedures given in the laser printer user manual before attempting to use the procedures described in this chapter.
Caution: some procedures in this chapter require the examination of the photoreceptor. The photoreceptor is light sensitive and should not be exposed to light for long periods. Do no expose a photoreceptor to light for more than a few minutes or print quality may deteriorate.
WARNING: some procedures in this chapter require examination of the fuser or fuser cleaning pad. The fuser is very hot when operating. Before examining the fuser or fuser cleaning pad switch the printer off and allow the fuser to cool for at least 15 minutes.
WARNING: a laser printer contains high-voltage components. Always switch the printer off before attempting any cleaning or maintenance procedure.
Print Quality Problems
There are a variety of print quality defects which occur from time to time in laser printers, most of these are extremely simple to rectify.
If a page has “fuzzy” print, letters or graphics which are not as sharp and clean-edged as usual, the problem is probably not the printer, but the paper. Fuzzy print is normally caused by printing on slightly damp paper. Paper absorbs moisture from the air, so paper which has been stored outside its wrapper for a long time may be damp. Try printing on freshly unwrapped paper.
Fuzzy/Faint White Lines
If a page has a fuzzy white line all the way down it, where the print is faint or absent, the transfer corotron is probably dirty. Open the printer and look carefully at the transfer corotron for particles of toner or dust from paper, these disturb the electrostatic field around the corotron so that toner is not attracted from the photoreceptor onto the paper. Follow the procedure described in the user manual to clean the corotron, most small printers require the corotron wire to be gently wiped with a cotton bud or a special corotron cleaning tool. Corotron wires are very fine and delicate, so be very gentle when cleaning the wire or it may break.
Sharp White Lines
If a page has a clearly-defined white line all the way down it, where print is absent, there is probably a blockage in the developer unit which is preventing a small area on the developer roller from receiving toner. The developer roller normally has blades (called “doctor blades”) immediately above and below it which scrape off excess toner, and a small lump of damp toner may block the gap between one of these blades and the developer roller. If possible examine the developer roller (this is not possible on printers using print cartridges) for a line on it which has no toner. Some printers are prone to this problem and supply a small cleaning tool which slides along the gap between the blade and the developer roller. If the user manual gives instructions for this problem, follow them.
If no instructions are given and the developer roller is visible it is sometimes possible to remove the blockage by gently sliding the corner of a sheet of paper between the developer roller and the blades. If the developer unit is a user removable part (i.e. without using a screwdriver to disassemble the printer), either on its own or as part of a toner/developer cartridge or print cartridge, lift it out of the printer and shake it from side to side.
Variable Print Density Across The Page
If the print density (the degree of blackness) varies across the page, it may be caused by several factors.
In general, when toner is running low the toner may not flow as freely as in a full toner hopper, so some areas of the page may get less toner than others, causing a variation in the print density across the page. To overcome this, fill the toner hopper. If the printer uses a toner or print cartridge remove the cartridge from the printer and, holding it horizontally, shake it from side to side four or five times to redistribute the toner.
If one side of the page is always lighter than the other, the printer may be unlevel. Check that the printer is on a horizontal surface, otherwise the toner may gradually move to one end of the toner hopper. Shake the toner hopper/toner cartridge to redistribute the toner. Another cause of one side of the page being lighter than the other may be light entering one side of the printer housing; most printers are not totally light-proof, and if they are placed near a strong light source (a lamp or a window) some light may leak in, affecting the photoreceptor. If the printer is close to a light source, move it to another location.
Variable Print Density Down The Page
If the print density varies regularly down the page to cause a “banding” effect, contacts on the photoreceptor or developer roller may be dirty. Some photoreceptors and developer rollers have a strip of exposed metal at each edge which is used as an electrical connection, if dirty, these strips can be cleaned using a cotton bud to improve the connection.
Clean these connections gently, taking great care not to damage the photoreceptor or developer roller surface.
If the print is grey rather than black, there are two likely causes, the print density setting and the photoreceptor.
Most small laser printers have a print density control, either a knob or a setting on the control panel. Increase the print density setting to make the print “blacker”.
As a photoreceptor wears out it holds less charge, transfers less toner from the developer to the paper, and hence causes grey prints. To overcome this the normal action is to increase the print density setting, until the photoreceptor requires replacement. If the problem is particularly acute it may be worth replacing the photoreceptor prematurely.
Grey print may also be caused by the low air density found at high altitudes. This is incredibly rare, but some models of laser printer have exhibited problems in high altitude locations in South America.
If the page is contaminated with toner on the blank areas of the page the paper will have a faintly grey appearance. This is normally caused by excess toner because the print density setting is too high.
Most small laser printers have a print density control, either a knob or a setting on the control panel. Try reducing the print density setting to remove the grey background.
In some printers a black page can be occur when the charger corotron is broken or not properly connected. Examine the charger corotron to see it is broken. If the charger corotron is broken and is part of the print cartridge or photoreceptor unit, replace the print cartridge or photoreceptor unit with a new one. If the charger corotron is not broken, or cannot be seen to check, try removing and reinstalling the print cartridge or photoreceptor unit, as the electrical contacts between the removable unit and the main part of the printer may not be connecting properly.
In some printers a white page can occur when the transfer corotron is broken or not properly connected. Examine the transfer corotron to see that it is not broken. If the transfer corotron is broken a service engineer will probably be required to fix it, as the transfer corotron is usually built into the main body of the printer. If the transfer corotron is not broken try removing and reinstalling the printer consumables such as the toner cartridge and photoreceptor cartridge or the print cartridge.
Regularly-Spaced Spots (Large Interval)
If pages have spots on them which are regularly spaced down the page with a large interval between each spot (several inches) there is probably a scratch, hole, small dent or other flaw in the surface of the photoreceptor. If the photoreceptor is removable, examine it. If a flaw is found, replace the photoreceptor or print cartridge. If the photoreceptor is not removable it may be necessary to call a service engineer.
Regularly-Spaced Spots (Small Interval)
If pages have spots on them which are regularly spaced down the page with a small interval between each spot (probably less than 3 inches) there may be a deposit of toner on the fuser. Switch off the printer and allow the fuser to cool for at least 15 minutes. Examine the fuser cleaning pad for encrusted deposits of toner, and replace the fuser cleaning pad if necessary. It is not usually possible to examine the fuser rollers themselves, if the problem persists it may be necessary to call a service engineer.
Random spots are normally caused by dirt and spilt excess toner in the printer mechanism. Remove all consumables, clean any toner off the consumable housings, and clean any toner from the insides of the printer with a tissue. Be careful to avoid brushing toner onto the corotrons.
If a part of the image is faintly “echoed” further down the page, either the print density is too high, or the photoreceptor is wearing out.
Most small laser printers have a print density control, either a knob or a setting on the control panel. Try reducing the print density setting to eliminate residual images.
If the problem persists, the photoreceptor is probably worn out. Replace the photoreceptor or print cartridge.
Toner Rubs Off
If the toner can be removed from the paper by gentle rubbing or brushing, it has not been properly fused. There is probably a fault in the fuser which is preventing the fuser from reaching the correct temperature. Call a service engineer.
Mechanical problems, such as misfeeds and paper jams, are normally caused by the media being used in a printer rather then the printer mechanism. The following are typical problems.
A misfeed occurs if the printer fails to feed a sheet of paper from the paper feeder. Misfeeds are normally caused by paper which is unsuitable for the printer, either because it is too light, too heavy, or too smooth, however misfeeds do occur with the correct paper.
If a misfeed occurs, remove the paper from the paper feeder, and fan the paper so that sheets are not sticking together. Reload the paper ensuring that the curl is loaded as specified by the printer manufacturer.
Repeated misfeeds sometimes occur because the springs in the paper tray which push the paper upwards onto the paper feed roller have become weak, in which case try loading more paper into the tray so that the springs are more compressed, and have the tray springs replaced or obtain another tray.
On some designs of printer it is possible to insert the paper tray inaccurately, so that it is not seated properly. Remove and carefully reinstall the paper tray so that it is pushed all the way into the paper feeder.
Repeated misfeeds may also occur because the rubber surface of the paper feed roller has worn smooth. If the roller which feeds the paper out of the tray can be seen and reached it is sometimes possible to gently roughen the surface of the roller with emery paper, otherwise a service engineer will be required to rectify the problem. Alternatively, the paper may be slightly too large for the paper tray, if the paper is a very tight fit in the paper tray, and difficult to load, it is probably not exactly the right size. Paper is sometimes cut inaccurately.
A paper jam occurs if a sheet of paper gets caught in, or refuses to pass through, the printer mechanism. A paper jam may be caused by paper which is too heavy or too light for the printer, or by damp paper, however many paper jams happen for no apparent reason when using the correct paper.
If a paper jam occurs, carefully follow the procedures in the laser printer user guide to remove the jammed paper. Pay particular attention to instructions which require the paper to be removed in a specific direction, as the paper may have loose toner on it which has not been fused and which may contaminate the printer mechanism. Paper may also be jammed between paper feed rollers or in the fuser rollers, attempting to pull paper in the wrong direction through these rollers will probably tear the paper.
Always remove jammed paper slowly, do not snatch the paper from the printer mechanism, or pull fiercely, as the paper may tear. When a sheet of paper has been retrieved from the printer, examine it to ensure that the whole sheet has been removed, if a small fragment remains in the printer it will probably cause another paper jam.
If repeated paper jams occur there is probably an obstruction in the paper path, the most likely cause is a small fragment of paper left by another paper jam.
If the image printed on the page is not correctly aligned with the paper, i.e. the image is skewed, the probable cause is incorrect paper loading or paper tray installation.
Remove the paper from the paper tray, fan the paper, and reload it into the tray, ensuring that the paper is correctly inserted below the “snubbers”, the small catches which hold the paper down in the tray. Ensure that the paper is a good fit in the tray, if the paper is able to move significantly (any more than a millimetre or two) then either the paper, or possibly the tray, is the wrong size. Paper is not always cut to size as accurately as it should be. Carefully reinstall the paper tray, ensuring it is pushed fully home into the printer on both sides.
If the printer uses an adjustable paper tray, ensure that the paper guides are closed snugly against the paper so that no lateral movement is possible.
Sometimes paper creases in the printer. The most common cause of creases is damp paper, sometimes a crease is simply a paper jam, skewed print or misfeed which didn’t quite happen. Replace the paper, and if the problem persists check all the potential causes of misfeeds, paper jams and skewed prints listed above.
If the image on the page is incorrect there may be an error in the commands sent by the computer to the printer, or the printer may have misinterpreted the commands or be incapable of processing them.
Garbled (Rubbish) Data
If data is garbled, and meaningless strings of text appear on the page, the most likely cause is a communications error. A small communications error occurring when a command is being sent to the printer can affect the formatting of all the data following the command, and a major communications error will affect any data sent to the printer.
Check that the cable connecting the printer to the computer is correctly plugged in, reset the printer (normally by switching it off and on), reload any downloaded fonts, and reprint the job.
If the data is still garbled the communications settings may be incorrect, particularly if serial communications are used. Check the communications settings on the printer and the computer, ensuring that they match. If possible reset the computer (the software controlling the computer communications may have crashed). If the problem remains, try another communications cable, and if possible try using the printer with another computer.
Print a status sheet, on most printers there is a function available via the control panel to print a status sheet. If the status sheet is garbled the printer controller is probably faulty.
If characters are occasionally missing from the text there is probably a communications error.
Check that the cable connecting the printer to the computer is correctly plugged in. Check the communications settings on the printer and the computer, ensuring that they match. Try using another communications cable. If a serial connection is being used, try setting the serial baud rate to a lower speed.
If text appears in the wrong font, or an unexpected font, it may be caused by a communications error, a software error, or a missing font. Occasionally a wrong font on a page may be caused by a fluke communications error, try reprinting the page. If the problem persists, check that the intended font is loaded in the printer.
Ensure that any font cartridges are correctly plugged-in, and print a font listing (on most printers there is a function available via the control panel to print a font listing).
If the desired font appears on the font listing ensure that the computer software application is correctly set up, and that the correct options are set in the printer driver.
If the font does not appear on the status sheet and is a downloaded font, reload the font. If the font is a cartridge font, examine the font listing to see if other cartridge fonts are missing. The cartridge may be faulty of have a broken connector. If the missing font is supposed to be a resident font a service engineer may be required.
If the problem persists, and the font is shown on the printers’ font listing, there is probably a configuration problem in the software application on the computer.
Split Graphic Image
If a graphic image is split over two pages, the most likely cause is that the printer does not have enough memory to process the page. This may be because extra optional memory is required by the printer to process complex pages and large graphics, or it may be that part of the memory in the printer has failed.
If the problem occurs repeatedly, check that the printer has adequate memory, and add optional memory if required.
If the printer has adequate memory, remove and reinstall any memory upgrade options. Print a status sheet, the status sheet normally shows how much memory is installed, and operate the self-test function of the printer to see if any memory errors are reported.
If text is split over two pages there is probably a configuration error in the software application sending the text. Check the software application setup to ensure that the page length and margins are correctly set.
Split text is very rarely caused by the printer, but it may occur if a page contains a very large number of characters and there is insufficient memory in the printer to cope. For instance a complete page of 6 point text contains many more characters than a page of 10 or 12 point text, and may exceed the capabilities of some printers.
If a split occurs on a page such that there is a horizontal gap in the image across the page splitting graphics and characters, the printer controller has probably made an error. This may be an occasional random occurrence, in which case the only solution is to reset (switch of and on) the printer, or it may be a frequent occurrence. If the problem happens frequently the cause is probably that either the printer controller or the memory in the printer controller is faulty.