Introduction To Laser Printer Image Defect Problems and How to Identify Causes of Image Problems
- William DeMuth
- Oct 31, 2019
- 7 min read
Updated: Nov 6, 2019
If half of all printer service calls are for jams, then fully one-third of them are for image problems. Actually, image problems are even more extensive than that, but many are handled without the aid of a technician.
It's no secret that most image problems are caused by cartridges, either new or refilled, and that many customers have learned to try changing the cartridge before calling the technician. With that in mind, the number of machine failures caused by image problems may equal those caused by jams.
It is important to note that even if the imaging system is working perfectly, image problems will still occur. Because paper path problems often cause imaging problems, it's important to develop a system for classifying and troubleshooting image problems
THE TONER CARTRIDGE
With virtually any image problem, it is usually a good idea to try another cartridge Often, the "signature" of the original complaint will fail to appear with the second cartridge, indicating cartridge failure as the source of the problem. This can be true, even if the second cartridge is unacceptable as well (it will likely be unacceptable in a different way). With that in mind, let's take a look at cartridges, how they work, and what can go wrong with them.
Toner Cartridge Parts Printers without one-piece cartridges frequently divide the cartridge's functions as two assemblies -a Developer Unit with the toner supply, and a Scavenger Unit, which carries the Organic Photoconductor (OPC) and gathers and stores the waste accounting for a rising share of the market, or can be, done to each of these parts as So toner. Refilled toners are once more we'll take some time to discuss what is, prepared for reassembly.
The Developer Unit The Developer Unit is also equipped with a method for delivering the toner to the OPC. The Developer Roller, or "Mag" Roller, consists of a permanent magnet core, surrounded by a thin-walled aluminum sleeve.
Toner manufacturers reacted to the unique properties of the new carbon-coated sleeves, new formulations produced much denser prints and have ever since. Today, it is impossible to remanufacture a cartridge that will duplicate the electrostatic balance of an OEM cartridge. In most cases, they can get pretty close.
Contacts, seals, bushings and a doctor blade round out the parts list for the Developer Unit. Most Developer Units, both in new cartridges and refills, rarely have problems. Although things can go wrong poorly gapped, toner can clump and inhibit development, deoxidizing compounds cal foul the bushings a Doctor Blade can be improper usually, the developer can be relied upon to operate properly.
Toner remanufactures, wanting to prevent surface oxidation from causing ghosting, often treat the Mag Roller Sleeves with special compounds. Should the refiller attempt to treat the sleeves while they are still mounted on the developer, he runs the risk of fouling the bushings, Rather than cause jams or poor mechanics, these chemicals within the bushings will produce distorted images everything from fisheyes to gray background
Developer Unit Toner has a ferrous component that causes it to adhere to the Developer Roller, which has a permanent magnet core. The toner is held to he proper depth by the Doctor Blade that is set a measure distance from the face of the rollers sleeve.
The Drum Unit
Most of the critical electrical activity happens within the Drum Unit. It contains the Organic Photoconductor (OPC), Primary Corona Assembly, Wiper Blade, Cleaning Blade, and Waste Bin. Cartridge problems generally start and finish here.
Drum Unit. The image is formed on the OPC (Organic Photoconductor), first, electrostatically, then (after development) in reverse with the former. Some of the problems with recharged cartridges are caused by improper handling of the disassembled drum units.
The OPC is the most vulnerable item in the entire toner cartridge. Unfortunately, there has been a practice of "use-until-failure" in the toner in the remanufacturing industry, a practice that has persisted until the present.
Competent remanufactures routinely replace components on schedule, others continue to use everything until it fails., Unfortunately, the failure is generally in a customer's machine.
While there are methods for salvaging the drum recoating and reusing absolutely not reusable in the condition attained after the first cycle Third-party "Super-drums" is in many ways technically superior to the OEM drums. Their polycarbonate coating is identical to the sort of coatings used for high-capacity copiers. It is harder and has a much longer service life The primary concern for service performance has a lot to do with why they are called "Super." They print darker, using the same toner than the OEM drums op
The only explanation for this must be the ability to accept and hold a charge. During the conditioning stage of image formation, the Primary Corona Wire has a -6,000 volt DC charge sent through it. Because there is no return, no complete circuit, the uninsulated wire conducts negative high-voltage electricity.
The result is ionization of the air around the wire. The ionized air moves outward through the varistor grid on the cover of the assembly, then brushes against e OPC, charging it to between -600 and-690 volts DC, the varistor grid supposedly bleeding off excessive charges.
There is nothing sacred about that number; it's just what it happens to be for that particular OPC coating. My belief is that the Super-drums do, in fact, receive a greater charge from the Ionized air and that the contrast in charge to discharged area promotes a darker print. (This is not the way the machine density control makes prints darker. The density adjustment controls the AC Bias that drives the toner towards the OPC from the Developer.)
OPC-Related Image Problems Whatever the situation with the OPC, the drum's performance is critical to the success of the cartridge. There are several common failures:
Right-Side Streaking-- This has nothing to do with the OPC. If there is a minimal amount of debris on the wire, the varister grid will produce equivalent ionization in the area of the OPC, and no harm is done. If the deposits are heavy, the drum will not be charged in that area and, during developing, that uncharged area will attract toner.
Fine Line, Vertical-- Sometimes, an abrasive particle Scavenger Unit, wedging against the OPC. As the drum rotates, the charge transport layer is ground against this particle and begins to scar. When the particle or accumulation of particles is particularly large, the scarring can cause the drum to quickly lose its conditioning charge in that area. The result is a line down the page that looks almost as if it had been formed by a set of instructions from a graphics catches on the edge of the wiper blade within the program.
Smudged Line, Horizontal Unless it looks like a formed line from a graphics application input, all horizontal lines are indicative of Wiper Blade failure or an overfilled waste bin. Generally, these lines will go only partially across the page and will be about 1/8-inch wide. It may be accompanied by other smudges.
Drum Divots--This problem occurs more commonly with Super-drums than with OEM drums. Because the polycarbonate coating is harder in the Super-drum, it is also more Brittle. Any little tap will cause it to "ding," opening a divot or hole. One prime suspect in this category is the drum cover frame. The drum cover is spring-loaded, and when it closes, such as when it is taken from the machine, the closure can result in an impact between the support rod and the surface of the OPC. When this happens, the divoting conditioning can occur. On the page, this reveals itself as a black group of dots that repeats itself three times on any given page. Any defect on any roller will produce a repeating pattern as a function of the circumference of the roller.
Exposed Drum--If the OPC is exposed to an excess of light, the ability of the Photoconductor to accept and hold a charge is compromised. In many cases, this can lead to permanent damage and loss of photosensitivity, manifested as dark areas on the printout, usually along the edges. Horizontal striping is also possible under some exposure coating itself. In other cases, the overexposed OPC will not print anything in the circumstances. With some OPCS, exposure actually changes the color of the drum damaged area, leaving some blank space in the output.
Light Print As the OPC ages, it becomes somewhat less conductive. It still may be capable of accepting and holding a charge, but it holds less and less of it. Correspondingly, the grounding of charge under light may lose efficiency. In a new OEM drum, the remaining charge is about -25 VDC after writing exposure. If the residual charge is greater in a fatigued drum, the resultant image will be somewhat fainter. Toward the end of a cycle, this is compounded by the quality of the toner. In any application, the most electroactive toner transfers to the OPC first. As the toner supply dwindles, the electrostatic balance shifts towards ever-diminishing transfer rates. Complicating this is the diminishing efficiency of the Mag Roller Sleeve in the presence of oxidation.
Toner Cartridge Problems
Cartridge problems fall into two categories. Either they produce a poor image or they dump toner into the machine. Refills and OEMS have somewhat different characters. The Refills are a bit more likely to dump toner and a little more likely eyes.
HP LaserJet M601 M602 M603 M604 M605 M606 Printer Components -- Distance between defects
Primary charging roller 37.7 mm (1.5 inches)
Transfer roller 47 mm (1.85 inches)
Developer roller 63 mm (2.5 inches)
Tray 1 pickup roller 63 mm (2.5 inches)
Tray 1 feed roller or Tray 1 separation roller 79 mm (3.1 inches)
Tray 2 feed roller, Tray 2 pickup roller or Tray 2 separation roller 79 mm (3.1 inches)
Printer Fuser sleeve unit or lower pressure roller 94 mm (3.75 inches)
Photosensitive drum 94 mm (3.75 inches)
Other Helpful Laser Printer Technical Support Resources
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