In order to understand and troubleshoot a Laserjet printer, I think it is important to understand how the printer functions. Laser printers for the most part contain some standard assemblies: Toner cartridge, Laser Scanning Assembly, High Voltage Power Supply, DC Power Supply, Paper Transport Assembly, Transfer Corona Assembly, Fusing Assembly, Printer Controller Circuitry, and Ozone Filter.
A laser printer undergoes a six step process that helps form images on paper. The six major steps are:
- This is the first step in the process in which a rubber blade inside the printer cartridge scrapes any toner left on the drum into a used toner receptacle inside the cartridge. A fluorescent lamp discharges any remaining charge on the photosensitive drum (the photosensitive drum or EP drum loses its charge when exposed to light).
2. CHARGING- A special wire called the charging corona within the toner cartridge located above the photosensitive drum receives a high voltage from the High Voltage Power Supply. This high voltage is used to apply a strong , uniform negative charge to the surface of the drum.
- The laser is turned on and scans the drum from side to side, flashing on and off according to the bits of information the printer controller sends as it communicates the individual bits of the image. Where ever the laser touches, the photosensitive drum's charge is reduced to a slight negative charge. As the drum rotates, a pattern of the exposed areas is formed, representing the images to be printed.
- Now the surface of the drum holds and electrical representation of the image being printed. Toner can now be transferred to the areas that were exposed in the writing step. A metallic roller called the developing roller inside the cartridge now acquires a charge from the HVPS. The toner sticks to this roller because there is a magnet located inside the roller and because of the electrostatic charges between the toner and the developing roller. The developing roller rotates toward the EP drum, the toner comes between the the developing roller and EP drum and is attracted to the areas that have been exposed by the laser and the toner is repelled by the areas that were not exposed to the laser. The EP drum continues to rotate until the developed image is ready to be transferred to paper.
- The developed image into position. The controller notifies the registration rollers that the paper should be fed through. The rollers move the paper underneath the EP drum, and the transfer process can begin. The controller sends a signal to the corona wire or corona roller (depending on which the printer has) and tells it to turn on. The corona wire/roller then acquires a strong positive charge from the HVPS and applies it to the paper. Now that the paper is charged, it pulls the toner from the EP drum and the line of contact between the roller and the paper. Once the rollers move the paper past the corona wire, the static-eliminator strip removes all charge from that line of paper.
- This is the final step in the process where the toner image is made permanent. The roller push the paper toward the fuser rollers. The fuser rollers grab the paper and is now in control of the paper. As the paper passes through the fuser, the 180 degree fuser roller melts the resin of the toner, and the rubberized pressure roller presses it permanently into the paper. The paper continues on through the fuser and then exits the printer.
The following picture will give you a general idea of the process and components.TROUBLESHOOTING: PAPER JAMS
- These are by far the most common problem encountered by all printers at one point or another. Some common causes of paper jams are as follows:
1. The paper is wrinkled or has upturned edges, the wrong type of paper is used, the paper is not place properly in the feed tray (usually not even).
2. If paper jams start happening at a frequent rate then the problem could be a worn roller (which can be replaced and are not that expensive). The following pictures shows the rollers.
3. Anther cause could be related to the drive gear of the pickup roller, shown here:BLANK PAGES:
If your printer is printing nothing but blank pages, then the toner is not being put on the paper. There are three major causes for this happening.
1. The toner cartridge could be empty or if you have just bought a new cartridge it is possible that you purchased a defective one. If you forget to remove the sealing tape the toner will not be able to be accessed properly by the printer.
2. The Corona Assembly could have a malfunction such as a missing or damaged corona wire. If this is the case the developed image will not transfer from the EP drum to the paper. The following is a picture of Corona Assembly:
3. Another cause is the High Voltage Power Supply. If the power supply does not charge the components with the proper voltages. Picture of an HVPS:REPETITIVE SMALL MARKS OR DEFECTS:
This usually happens with heavily used or older laser printers. The following could be causing the problem.
1. Toner may have been spilled inside the printer.
2. A chip or crack in the EP drum can be another cause which can cause a toner build up and can get stuck on one of the rollers. EP drum picture:VERTICAL BLACK LINES ON THE PAGE
This can be caused by the following:
1. A groove or scratch in the EP drum.
2. A dirty Corona Wire which prevents a sufficient charge from being placed on the EP drum.VERTICAL WHITE LINES ON THE PAGE:
The number one cause is the following:
1. This usually happens when proper cleaning and maintenance is not performed on the printer. Foreign matter gets caught on the transfer Corona Wire. IMAGE SMUDGING:
This happens when you pick up a paper that has just come out of the printer and when you touch the ink, it smudges or smears.
1. The fuser could be malfunctioning or need replacement due to a burnt out halogen light inside the heating roller.
2. Dents or cold spots in the fuser heat roller can also cause the problem.GHOSTING:
Ghosting is what you have when you can see light images of previously printed pages on the current page. Usually one of two things cause this problem.
1. Bad erasure lamps. This causes the previous electrostatic discharges to not be completely wiped away.
2. A broken cleaning blade. This causes old toner to build up on the EP drum and presents itself in the next printed image.PRINTER PRINTS PAGES OF GARBAGE:
This happens when the print on the paper comes out like garbage and is not understandable or looks like some government secret code on the page. The following are usually the causes.
1. The printer driver software is not the proper driver for the printer or it is not configured for the correct page-description language (PCL or PostScript).
2. A bad formatter board. Remember the formatter board receives information from the computer and turns it into commands for the various components in the printer.
The following are some extra pictures to gain a better idea of some of the terminology used in this tip and get a better view of its components.
Close up of Laser Assembly and mirrors:
Laser diagram on how the process works:
Separation pad where pickup roller attached:
Common Fuser Parts:HP LASERJET ERROR MESSAGES:
00 Ready--The printer is in standby mode and ready to print.
02 Warming Up--The fuser is being warmed up before the 00 ready state.
05 Self Test--Full self test has been initiated from front panel.
11 Paper Out--The paper tray sensor is reporting no paper in tray.
13 Paper Jam--A piece of paper is caught in the paper path. Open the cover and remove any jammed paper and close the cover.
14 No EP Cart--No EP cartridge (toner cartridge) installed in the printer.
15 Engine Test--An engine self test is in progress.
16 Toner Low--The toner cartridge is low. Replace the toner soon.
50 Service--A fuser error has occurred. Commonly caused by a fuser lamp failure.
51 Error--Laser scanning assembly problem.
52 Error--Scanner motor in laser has malfunctioned.
55 Error--Communication problem between formatter and DC controller.