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Shorter Article on Fusers.
Fusers |
Fusers are an essential part of laser printers, they melt and press toner powder into the page. Fusers can be built to be long lasting, but ultimately they wear out and sometimes they degenerate suddenly making the printer unusable.
Printer users know that if they don't have a spare toner cartridge they isk having a printer that won't work. A fuser usually lasts a long time and is expensive so people are less likely to keep one ready for the inevitable problem.
Unfortunately there are thousands of models of printer and the IT service industry only tends to keep fusers for the most common machines on the shelf. For less common models there may be just one warehouse with stock in Europe or worldwide. Fusers may even be made on demand - hence the long lead times sometimes given.
Still more annoyingly most printer makers subcontract the work of making fusers and when the contract changes shortages can last months. This happens to some big brands at times.
Fusers fail for two reasons:
- over a long time they wear out and the printer will announce that the fuser life has expired. Small cheap printers can have a fuser life as low as 50,000 pages. Large printers typically have fusers that last 250,000 pages or more. The printer will often keep going with a message to change the fuser permanently on the display.
- the fuser may suddenly fail, for instance when a foreign object passes through the printer and destroys it. The fuser is essential and the printer cannot work again until it is replaced.
Toner cartridges for the main printer brands are fairly readily available both from the original printer manufacturer and often from some competing makers and from refillers as well. Fusers have a lower demand so they are less readily available. Most of the main printer manufacturers do sell fusers for a price that makes them worth eplacing.
Some manufacturers price fusers to suggest the user might like to buy a new machine instead. There may be alternative manufacturers parts for these machines. There may also be a choice of using a efurbished fuser. However you probably won't be able to buy a fuser straight away from a high-street shop.
Some printer manufacturers don't make fusers readily available at all for some models. If a fuser cannot be replaced in a timely fashion the printer may be little better than scrap. Availability of spares is something to take into account when buying a machine.
The rest of this article explains what a fuser is, the constraints designers are aiming to meet, how different designs work and why a fuser will wear out. It also gives some ideas on what might be going wrong if a fuser doesn't seem to work, on the quality of refurbished fusers and on why manufacturers tend to charge rather a lot for replacements.
Laser Printer Process in Outline |
The fusing process is the last of a series of stages that create a printed image on the page. This section outlines the process very briefly.
Almost all recent "laser printers" use a process called dry process electrophotography. Static electricity and light are used to deposit fine particles of coloured toner powder so as to make up a picture. The fuser then melts and presses the toner into the page.The process goes along these lines:
A photoconductive drum or belt held in a dark place is given a strong electrical charge . In the picture here it is a drum rotating clockwise.
A sequence of operations take place around the drum. Starting at the top it is first given a strong electrical charge by a rubber roller or a charged wire called a corotron.
A laser scans across the photoconductor and areas lit lose their charge, it drains away into the metalwork of the drum. The drum now has a latent image in charged and uncharged areas.
The photoconductor moves opposite a "developer" carrying electrically charged toner powder. Toner powder is attracted to the photoconductor according to the charge it carries and is repelled from areas where it shouldn't adhere.
The photoconductor moves to a transfer station with another static charge. The toner is stripped away from the photoconductor and onto a sheet of paper. The paper was driven out of the tray by the pickup oller as the drum started to rotate. The photoconductor goes on through a cleaning station and is used again.
The paper now carries an image in toner powder, loosely held by static electricity. The image isn't yet fixed to the page, that is the job of the fuser.
The fuser fixes the toner to the page using heat, pressure or both. Most toners are plastic, wax or resin (or a combination) so they melt at temperatures of 150 to 200 centigrade. Paper would distort and discolour if it were exposed to these temperatures for long, but it is usually in contact with the fuser for a fraction of a second so no harm is done.
The fuser is the last stage in the printing process. After it there are rollers to direct pages to face-up or face down trays and big printers have multi-bin sorting, staplers and booklet stitching. However if the fuser isn't working correctly pages will be ruined.
Fuser Mechanisms: |
Fusers come in two main types: hot rollers and foil. The foil mechanism is an improvement developed in response to the high power consumption characteristic of the hot roller mechanism.
Hot Roller: |
The traditional fuser design uses a heated roller on the top and a pressure oller underneath. Paper and lose toner pass between them and softened toner is forced into the paper at the nip point.
Heated rollers are a metal pipe usually about 30-40mm in diameter with a wall 1 -2 mm thick. The metal is usually aluminium, which is mechanically quite strong, highly conductive thermally and electrically and won't rust. The heater is a tungsten-halogen lamp running through the middle of this tube. The inner surface of the roller is coated to absorb heat and light. The outer surface of the roller is coated in something so that the toner and paper don't stick to the oller. The outer coating might be silicone rubber, can be an oil but tends to be a fluorocarbon polymer such as polytetrafluoroethylene (ie Dupont"Teflon") . This heated oller is driven round at a speed matching that of the paper passing through the fuser by a cog at one end.
The temperature of the roller needs to be quite closely controlled. The sensor is usually a thermistor held against the outer surface of the hot roller surface just before the point where it will touch the paper. Readings from this thermistor feed back to the engine controller board and are used to turn the lamp inside the roller on and off keeping the oller surface at the required temperature. When the machine is printing and the stream of paper is cooling the roller the lamp tends to be on for long periods. When the printer is idle is tends to light every ten seconds or so as conduction and convection cause cooling.
Pressure Roller: |
The pressure roller is just a big silicone rubber roller on a metal shaft. The pressure roller is held in tight contact with the heated roller by springs. The pressure roller turns with the heated oller and the paper passes between them. At the area of contact the toner on the paper softens sufficiently to bond with the paper, but not sufficiently to run into it's flock and become smudged or stick to the hot roller and cause offset printing. The fuser designer and the printer's control firmware need to match the rate paper moves through the fuser, the number of pages per minute, the thermal capacity of the roller the power of the heater and the viscosity of the toner materials.
Oil and Toner Formulation: |
Hot roller fusers have worked well for many years in photocopiers. Copiers actually have another detail which is that the hot roller is often lubricated very lightly with silica oil fed from a bottle through a felt wick. Toner would still tend to stick to the roller if it weren't for this thin coat of oil. Some laser printers do this as well, normally using a replaceable felt wand that drops into the top of the fuser. The oil is potentially messy, people forget to replace the felt wand and there might be a health question about exposure to silica oil. Recent printers often eliminate the oil by using a microencapsulated toner with a lubricant component. The encapsulation process often produces more evenly shaped toner grains which are more responsive to the printers electrostatic fields giving improved print resolution and a grey scale - both of which improve photographic reproduction.
If a printer is used continually to produce very heavily printed pages or to handle coated media like labels and vinyls the fuser will wear out more rapidly. Some manufacturers (notably Lexmark) produce web-oiler fusers that will last longer in this kind of work.
Power Consumption: |
The main defect of the hot roller design is that it takes a couple of minutes to heat through from cold to working temperature. Users don't like to be kept waiting. To give users rapid print during a working day the fuser is often kept hot. Although the fuser needs to be hot other parts of the printer need to be cool, so the area round the fuser is commonly cooled by a fan. As a result the printer can spend its idle time acting like a small fan heater. Other problems are that the lamp is fragile and has a limited life. Roller coating materials aren't stable but age and decay, they decay more rapidly if they are hot but most rapidly if they are apidly heated and cooled.
Hot roller fusers tend to have a life somewhere between 50,000 and 250,000 pages. The limit on life is usually the heated roller coating which will wear through particularly where the temperature sensors touch it. The lamp will also fail at some point and ultimately the bearings will be worn out.
Most office printers tend to be used in unpredictable bursts several times per day with long gaps in between. The average print job is about 5 pages and the other mechanisms in a laser printer can deliver that amount of paper in seconds. A hot roller fuser can handle that volume of paper in seconds as well, if it is hot to start with. Keeping a fuser hot in a small printer which doesn't have space for a lot of insulation wastes electricity. The power used to heat the fuser can easily exceed 70% of total printer energy consumption. The alternative approach would be to have a fuser that could heat up very rapidly.
Rapid heating can be achieved in all sorts of ways; one might be direct infrared heating but that raises a possibility of fire. Fast acting fusers rely on having a more powerful heater and a thin walled roller. Because the thin walled roller has a lower thermal mass thermostatic control from the electronics needs to be quite good as well. This is the approach taken in Ricoh's Quick Start Up (QSU) printers, a thin-wall heated roller with dual heaters. The dual heaters also give flexibility as to how much heat is delivered so the engine controller can very rapidly heat the roller to near working temperature then fine adjust the heat with either or both lamps.
Foil: |
The ultimate thin wall hot roller is nothing but a foil wrapped around a heater.
Foil fusers replace the heated roller with a belt of much lighter material wrapped around a ceramic heater rod, both of them directly pressed against the paper. In this case the pressure roller rotates mechanically and the lightweight foil just rotates with it. Being light and thermally conductive the foil transfers the heat from the ceramic directly to the toner and paper.
The big advantage of the foil mechanism is that it can have a low thermal mass. The heater embedded in the ceramic can be just a pencil thin rod within a wider insulating bar or it can be supported on a metal rod. It can take under ten seconds from power up for the ceramic to each printing temperature. The foil is mainly there so that it can move with the paper and so the contact needed for rapid heating and softening of the toner doesn't smear the image. The foil's main job is to transmit the heat straight through from the heater to the paper.
Ceramic bar heaters are a well established technology - in a crude form they are used as room heaters and in a much more advanced form they are used as thermal print heads in bar code printers. The heater in a laser printer isn't usually very sophisticated, resistor wires embedded in the ceramic near the print surface. The thermistor and thermal cut-out can be incorporated in or near the ceramic as well.
The foil is a sophisticated material. It needs to be a thin, thermally conductive material that won't adhere to toner, paper or any of the other media the user might put through the printer. It also needs to be electrically neutral so as not to disturb the toner on the paper as it comes in range; so there might be a metallic backing layer both for strength and to discharge static. The material normally used is a teflon roll or belt which has the right thermal and non-stick properties. The foil needs to be as smooth as a roller would be at the nip point so it might be held under tension. A foil is slightly stressed as it starts and stops moving, and depending on the shape of the fuser it is also being flexed, so it will ultimately wear out. Any mechanical obstruction such as a staple accidentally dropped into the machine will destroy the foil. Foils often rip in the direction of tension. Foil failure is often referred to as delamination.
Foil mechanisms are used by Canon as part of their "on-demand" and by HP as "instant-on" technology. Early use of the idea was in the little desktop HP 5L printer which are often used just a couple of times per day so neither the bulk or energy consumption of a conventional fuser was justified. Canon and HP have developed the idea so that it is now used in all the smaller printers up to about 60 pages per minute - most of their office printer ranges.
Superficially the foil mechanism looks fragile, any differences in tension on the material would destroy it and rollers look more robust. The problem with non-stick roller surfaces is that the non-stick material which doesn't bond to toner or paper doesn't bond to the metal of a roller very well either. Non stick materials bond to themselves better than to the metal backing of a roller. Foil based fusers usually have lives equalling or exceeding those for roller based machines. Hot roller designs are still preferred on larger printers but that might be as much design conservatism as design need. Large printers are often in continuous use so the energy saving character of a foil is less important.
Other Designs: |
The hot roller design is old but still used. The foil design is commonplace as well perhaps because HP and Canon are two of the largest printer manufacturers. (And indeed they work together, hence the printers resemble one another). Ricoh's QSU design is mentioned above. Several companies including Canon, Konica Minolta, and Panasonic use induction heaters on various models. Another approach is to use a metallised belt or foil with an induction heater rather than a ceramic heater behind it. These other techniques involve complicated electronics so they are not very common in office printers at present.
Practical Fusers: |
A fuser's role in the printer and the two most common mechanisms have been described, but not an actual fuser.
There are as many fuser designs as there are printer designs, indeed there may be more.
Each printer engine has its own fuser design. Fusers tend to be based on a theme - hot roller or foil for instance but they are all somewhat different- the size of cogs, size of rollers, roller pressure springs, bearings, and fixing holes.
Each variant of a printer may have a fuser which probably only differs in the heating mechanism and thermistor coils. Having made a successful 20 page per minute printer the manufacturer will try to update the design to 25 ppm by increasing the engine speed and the fuser temperature. If the temperature can't be tweaked higher they can change the toner formulation to work at lower temperature. Later variants often have little modifications to the shapes of plastic and metalwork to eliminate weak points. Fuser metalwork may stay fairly constant across a range of printers but the heaters, sensors and connectors change with variants. For example the Lexmark Optra S 1200 series runs from 12 to 34 pages per minute with different models taking evised print cartridges and fusers.
Fusers also come in two versions, a 120 volt version for the US and a 220 volt version for Europe and most of the rest of the world. In Lexmark's case they often ship a 100 volt version for Japan as well. The assumption is normally to ship 220V versions in Europe but there are a few places where other values can be used - construction sites for instance.
If there are a couple of thousand types of printers there are several thousand types of fuser. Each fuser design has several variants of heater and thermistor for the voltage and the specific temperature. Unfortunately it isn't easy to swap heaters and thermistors so there are thousands of fuser designs but most of them are rarely required. Fusers are a logistics nightmare.
Basic Structure: |
The chassis of a fuser is usually a piece of punched, drilled and formed sheet steel about 2mm thick. Ordinary bulk plastics aren't obust enough at the temperatures used. A traditional fuser has a rubber roller in it's lower half and a hollow, heated, metal oller in the upper half. A foil fuser still has the heater, a pressure oller and possibly some support rollers.
Fusers typically come in two lengths to suit the paper path of the printer - about 8.5 inches to take the narrow side of A4 and letter paper or just over 11 inches to take the narrow side of A3 and tabloid papers.
The chassis supports the two rollers or a roller and the ceramic heater. The heater will need power and sensing information so there is some sort of electrical connection.
Older fusers often use flying-leads for the connectors - usually there is a large one for the power and one or two smaller connectors for the thermistor and paper feed sensors. The nice thing about this is that it's easy for a knowledgeable technician to test the fuser with a multimeter. A problem is that people sometimes trap the wires against metalwork as they are putting the fuser into the machine.
More recent fusers generally use a multipole connector mounted directly on the fuser chassis which mates with another on the printer body. The nice thing about this design is that the fuser is a plug-in unit that can be quite easy for user to change. However it's more difficult to decide which wires to test with a multimeter.
There are also typically:
- some paper guides and separators to prevent paper taking a wrong path and wrapping itself around a roller.
- paper feed sensors - usually one or two opto-sensors with flags that the paper pushes aside as it moves through.
- a sensor for temperature and an emergency cutout.
- a set of plastic covers intended to keep user fingers out of hot ollers and live electrical contacts.
Power Supply: |
Fusers are basically heaters for paper and heaters use quite a lot of power. Heating a rapid succession of sheets of paper to somewhere in the 150 -200 centigrade range consumes several hundred watts of electricity. Small printers ated at about 10 pages per minute tend to use about 300 watts and 50 page per minute machines can use a kilowatt or so when they are unning. Most parts of a printer run at low voltages, the motors typically use about 24 volts. Fusers use so much power when they are active that they are normally driven directly from the 120 / 240 V AC mains via a triac to switch the heat on and off.
This power consumption may sound quite high but compared to the price of paper and toner it isn't all that significant. A 60 page per minute printer running full-on for an hour has probably consumed about £70 of toner and paper but perhaps 10-20p worth of electric power. Inkjet printers use a lot less power, but more expensive ink.
The circuits controlling the fuser are often rather distinct from the est of the printer.
Fusers are electrical but not usually electronic. Microprocessors or electronic assemblies are rarely used on a fuser because temperatures aren't suitable. Any electronic control is usually moved to a board called the engine controller which deals with all the switches and motors and with power for the fuser. Sometimes the engine controller is separate from the power supply so there may be a link between them to turn the fuser heater on. In recent printers power supply and DC controller are often a single board saving space and money.
The fuser itself usually has a pair of high-current leads for it's heater. These run through a thermal cutout which will prevent the fuser overheating if the engine controller were to crash. If the fuser heater fails it normally goes open circuit and engineers commonly measure the resistance to check for this. Depending on the printer design a resistance somewhere in the 50 to 200 ohm range is expected.
A pair of low current sense wires come from the thermistor.
Fusers often do have one or two opto-sensors mounted on them so that the machine can sense paper movement and this usually explains any extra wires. Fusers might have pressure sensors, media type adjustments and multiple heater controls but these elaborations are used on bulk production machines rather than office printers.
Paper Jams: |
The fuser is one of the likeliest places for a paper jam to occur. Paper goes into the front of the fuser between the rollers. The paper and toner had a strong electrical charge when they passed through the transfer station but this is usually discharged after that. If the charges aren't correct the paper might deflect and crash into the fuser, typically getting turned into a concertina of darkened paper on it's front. A variety of paper guides and separators aim the paper between the rollers and attempt to stop it wrapping round them.If pages crash into the front of the fuser that suggests the charge on the page is wrong and that whatever discharges the page isn't working properly. Missing screws, paper dust - or the transfer roller itself is dirty and inducing the wrong voltage.
Printers have a series of paper movement sensors that tell the controller paper is moving as expected. The sensors are frequently opto-interrupter types - a U shaped plastic object with three or four wires leading back to the DC controller board. The paper actually pushes a "paper dog" or flag and that rotates another flag into the optical sensors path. When the controller sends a page it then watches the status of the paper dogs changing to track the page through the machine. Most fusers have a paper movement sensor on their exit and if a page doesn't arrive there at the correct time an HP printer gives "Error 13" (Other makes do something similar).
The paper dog on a fuser is often a bit unusual because fusers are a hot place for an opto-sensor to work, so the tip of the sensor arm is midway across the paper path then a long plastic rod connects it back to an opto sensor on the side of the fuser where things are cooler. If there is a serious paper jam users sometimes dislodge the sensor and its rod so it no longer moves freely. The rod might also be dislodged in shipment or handling. Usually they are easy to put back in place.
Paper can often exit a fuser in three directions - immediately out to a face-up tray, up to the top face-down tray or down and round to a duplex unit. At the same time a new page is often just being released from the registration station and a fresh page may be being picked up from the tray. If any of these fail the main engine usually stops, leaving a page half in and half out of the fuser.
Releasing a jammed page from the fuser is easy on most recent machines. When the printer lid is open a lever pushes the rollers apart against some springs. In some cases the lid also disengages the fuser rollers by lifting out one or more gears on something called a swing-plate assembly. The fuser rollers then turn relatively freely.
There can be a problem here that causes noisy printers. The lid of the printer closes sufficiently to make the safety switch and allow the printer to start but not quite enough to properly mesh the cogs joining the fuser to the main motor drive. The motor starts and makes an unusual noise as it slightly damages the cogs but the user fails to notice. After a little while each cog has a step in it that is barely perceptible visually but all too audible.
Drive Motor: |
In many printers the fuser drive comes from a main motor that also drives the various rollers and the toner cartridge. It is simple to keep all the parts synchronised via a gear chain where the ratios of the gears relate to the diameter of the rollers. Some recent printers don't have a main gear chain so they do have a separate fuser motor. Motors aren't usually part of the fuser itself because it would get hot but there are exceptions to every rule, see the Color LaserJet 2600 fuser which has it's own motor, albeit stuck out on a bit of a limb from the main body. Having a fuser motor separate from the paper feed is helpful because an error in the input stages doesn't need to stall paper passing through the fuser.
If the fuser doesn't have its own motor the fuser gears have to engage properly with the main body of the printer. Mechanical meshing is usually quite straightforward but some designs need a bit of a jiggle to get them to seat properly. Its advisable to make sure the gears do seat properly before screwing a fuser in because if metalwork is bent the fuser will never sit properly and there will be paper feed problems. As usual with computers never force anything to fit, the manufacturer is very unlikely to have made it wrongly.
Swing plates are sometimes used to connect the fuser gears to the main motor gear chain when the printer lid is closed. This is helpful to the user as it allows the fuser rollers to turn relatively easily when the lid is opened to clear a paper jam. a potential problem with some designs is that it is possible to close the printer lid sufficiently to operate the lid-open switch but not so as to thoroughly e-engage the gears between the motor and fuser. The printer will then become noisy because the gears are stressed and slipping but this might not be noticed in a busy office. The swing plate gears and perhaps those of the fuser and the motor gear chain get damaged and are then perpetually noisy or inclined to slip and give misfeeds.
Fuser Failure: |
There are more than a thousand designs of office laser printer. However there are just a few broad themes for fusers so it is possible to offer some guidelines on how to identify fuser failures and what to do about them.
Fuser failures are usually straightforward to diagnose: typically the printer announces a fuser error on its display panel or in the driver software. Sometimes part or all of the material coming out of the printer isn't properly adhering to the page. Sometimes there are marks on the page which correspond with some on the fuser roller.
Heater Failure: |
If a printer reports a fuser failure it is either that: -
- the printer's estimate of the fuser life has now been exceeded (actually the software writers estimate)
- or that the fuser heater that has failed; failure of the heater is something the printer can easily detect.
The print engine turns the heater on and gets on with other self test routines, turning the main motor and testing the scanner. After a while it checks for a temperature rise. If the fuser heater is broken and so the oller remains cold the engine controller will signal the failure after a minute or so.
Apart from the message there are two other indications that a fuser heater has failed - The fuser doesn't get at all hot when the machine is turned on. Be cautious about feeling the temperature of a fuser - don't just jab at things that may be very hot. If you can't sense any heat near a fuser then either it's got excellent thermal insulation or it has died. Almost all fusers have big labels saying "Caution - Hot Surfaces", they mean it. a live fuser usually has some detectable heat that can be felt without touching anything very hot.
The heater element usually fails "open circuit". It is possible to test whether the heater has failed with a multimeter. The power connector on the fuser is self- evident and usually has three terminals - earth, neutral and live. With the fuser out of the printer it is fairly easy to check the resistances. There should be no connection between earth and any other terminal, but a zero-ohm connection from earth to the fuser metalwork. The two other terminals will have a resistance somewhere between 10 and 100 ohms - the bigger the fuser the lower the esistance. Again a note of caution, unplug the printer and let the fuser cool before touching it. Manufacturers take precautions to make sure people don't get hurt but the fuser isn't guaranteed safe.
Roller Failure: |
Failure of a fuser foil is often dramatic - bits of foil emerge on a sheet of paper with lose toner powder on it. Within a few pages the thermal sensor sees the breakup of the foil and the fuser shuts down.
Failure of a heated roller is not usually dramatic, a mark will appear on the page at intervals of 30 - 50 mm depending on the fuser roller circumference. Fuser marks usually get progressively worse. If the mark isn't cleared by changing the toner and developer then the fuser is the next likely culprit. It used to be easy to spot fuser damage because the rollers were visible but on recent fusers things are more difficult because there is a lot of plastic shielding around the unit. The source of the mark is usually visible if the fuser is turned by hand, a bit of the teflon coat will be missing from the fuser oller. Once the roller coat develops a hole it will progressively degenerate until a dirty band extends down the page. Printers have no way to sense that the roller is degenerating so they are likely to just go on working, but the output will be spoiled by a vertical streak.
The heated roller can also fail less dramatically, just giving increasingly dirty pages with bits of faint print from elsewhere on them. Toner is sticking to the fuser roller. If it's a fuser that needs a silicone lubricant pad or web (now rare) then that might need changing. If there is no specific visible lubricant then either:
- The lubricant properties of the toner are wrong and toner is baking onto the roller. This is very unlikely if the print cartridge is a manufacturers original. It is possible if the cartridge has been ecycled because it will be quite difficult for the recycler to gauge exactly what toner should be used - if it is available to them at all. If the damage is not too great switching to a manufacturers original cartridge should clear the problem after a few hundred pages.
- The non-stick layer on the fuser roller is wearing out, this is likely if the fuser is coming to the end of its life. It is particularly likely if the margins of the page look dirty, a phenomenon known as "edgewear" caused by constant distortion by the paper edges. The normal replacement is the whole fuser unit.
There is another possible fuser problem that gives dirty pages. Using inappropriate grades of label or envelopes sometimes works - but bakes adhesive onto the teflon roller. In this case it may be possible to clean the mess off the roller using isopropyl alcohol or meths. Cleaning a roller is a tedious job because getting access to the roller is usually difficult. Sometimes a whole label sticks to a fuser.
Other Failures: |
Some other failures are possible.
Paper jams at the fuser are mentioned above. Most fusers carry at least one paper sensor flag which is usually a long plastic rod with an opto-sensor at one end. This needs to be free to move but sometimes they get dislodged either in transit or as the person installing a fuser picks them up.
One rarely seen but very annoying fault is a failure in the fuser drive circuit rather than in the fuser itself. The failed component is usually the triac that delivers power to the fuse heater. This fault might be spotted by metering the fuser heater resistance out of circuit as mentioned above - if it seems ight but the fuser won't work then something suspicious is going on.
Even worse is a fault the manufacturers guard against by fitting thermal cutouts or fuses onto fusers. A triac that has failed closed-circuit will just go on heating the fuser so the user may indeed get a couple of pages through it on switch-on. As the fuser temperature rises the thermal cutout operates to prevent a fire. Unfortunately a thermal cutout will re-make when the fuser cools down giving an annoyingly intermittent fault. A thermal fuse is better in some ways as it will just melt and leave an open circuit. On many ecent fusers the terminals for the thermal fuse aren't visible because they would be an electric shock hazard. The only way to distinguish a failed thermal fuse from a failed heater is to measure each of their esistances but fuser design doesn't make that easy.
It is difficult for the average field technician to deal thoroughly with these faults because the measurements that would give certainty involve getting meter probes onto carefully insulated terminals in a powered up printer carrying potentially fatal high voltages. Even very experienced technicians are likely to risk buying a fuser and failing to fix the fault rather than risk a fatal shock.
Both these cases are rare but worth knowing about because buying a new fuser won't fix the fault. Life is like that.
The thermistor is a potential failure point as well. These components are simple inside and designed for the temperature range they are used in so they aren't usually suspect. If the fuser temperature seems wrong it is far more likely that the connectors need reseating than that the thermistor is wrong.
If the fuser has been damaged by paper or labels wrapping round the rollers the thermistor might not be make contact and things will tend to overheat - the printer will sort-of work but the pages will be faded with some lose toner. On the odd occasion fusers are found to have a buff envelope tightly wrapped around them so from the outside everything looks perfectly normal - it's only when the device is dismantled it becomes evident that the fuser roller has been covered.
One of the commonest problems with a fuser is that connectors don't mate quite properly so reseating them should clear the fault.
New Fusers and Other Choices: |
Fusers used to be described as "engineer changeable consumables" and sometimes they still are. As already suggested there are lots of different designs. Some recent printers have fusers that are easily changed. Most fusers are not too difficult to fit. However manufacturers can also take the attitude that the fuser will last the commercial life of the printer and make the fuser expensive to buy, difficult to change or both.
The simplest way of estimating how easy a fuser will be to fit is to see how difficult it is to get the old one out. Inspecting the old fuser is often a good idea anyway, as some faults are clearly visible emoving all doubt as to whether a new fuser is needed.
If the fault is not visible then it may be evident using a multimeter. Determine which of the connectors carry the heater current (chances are that they are bigger than others) and determine the DC resistance. Heating circuit resistance is likely to be about 50 to 200 Ohms depending on the printer.
Maintenance Kits: |
Maintenance kits are available for many of HP's mono printers and for some other makes. HP generally don't make kits for colour printers probably because fuser life depends on page cover but roller life does not.
A problem with maintenance kits is that it isn't a solid idea so a manufacturer might supply a fuser maintenance kit and the extras supplied might be as little as an instruction sheet and a pair of protective gloves - not a set of rollers. On the other hand some manufacturers supply things like transfer rollers that often just need cleaning, not changing.
Service Codes: |
Manufacturers can make fitting a fuser into a technician-only job by insisting that some engineering codes are given before the fault message clears. Several manufacturers do this. The idea is that only qualified service engineers can change a fuser.
From the manufacturers point of view this has at least two advantages:
- End-users aren't familiar with the basic engineering procedures needed to change a fuser. Some make a hash of it. Giving telephone support to a user who has limited knowledge of printers and has never seen a fuser can be very difficult.
- Support engineers help make the eputation of printers. If the printer doesn't need a support engineer will they feel any obligation to the manufacturer? So using service codes has an element of preserving jobs for dealers.
The conflict here gets more difficult as printers become relatively cheap. The price of service calls tends to rise with time whilst printers become cheaper.
Maintenance codes are historically "secret" but on the web few secrets last long, so if the printer needs one it is usually discoverable.
Recycled Fusers: |
The manufacturer whose label appears on the printer often isn't the only source of fusers, Since some manufacturers don't see much value in providing spares and either don't supply them or supply at ridiculous prices alternatives are needed.The obvious thing to do with failed fusers is to recycle them. The two components most likely to fail are the roller or foil in contact with the paper and the heater, so if they are both replaced the fuser should be nearly as good as new.
There are a few problems.
Printer manufacturers may not choose to supply rollers, foils and heaters. This may not always be a problem because printers are like the automotive industry; parts may be available if the whole thing is not. The majority of printers sold have an "engine" which is made by a company that isn't on the printer badge. Of course the brandname may own some or all of the intellectual property of the printer and may have a right to determine what happens to the parts - or not.
Many parts are made by subcontractors who will make, say, 115,000 belts to meet an order for 100,000. The "overage" is intended to cover quality issues and test failures but many or most of them may be perfectly good. Manufacturers might specify that overage must be destroyed, or might let the subcontractor make a profit from selling good product in their own right. There is some "overage " both of components and complete fusers.
Worldwide there are a few hundred million laser printers in use so its quite a large market. If a printer type is common enough there are manufacturers of compatible or alternative parts. In the automotive industry there are some unbranded parts that shouldn't be used and other parts manufacturers who proudly claim their parts are better than the manufacturers original. In the printer industry likewise there are bad clones and good alternative parts.
It is possible for a parts manufacturer to make a teflon oller or belt that is actually better and longer lasting that the manufacturers original. However there is a question as to how we can be certain which is which without long practical experience. Clone component makers might give a longer warranty as a way of proving their good will.
Commercial recycling hits some practical limits. Stripping one or two fusers down and ebuilding them tends to be time consuming. Older simple fusers can be done quite quickly but newer models with all sorts of plastic covers and clips can be a slow job. The technicians in a repair centre might recycle their own fusers but doing so is a quiet-time job. Printer manufacturers see advantages in tying people into long warranties not in making fusers that are easy to repair.
Companies that specialise in fuser repair can have the assembly and test rigs and skills to do the job quickly. They are generally prepared to pay a small amount to get old fusers or "cores" as they are known in the trade. However they will usually only arrange collection on 20 or more cores and the price paid might just about cover the storage and administration costs of building a stack of old fusers waiting to go.
There is still a potential quality problem with recycled parts. The parts that clearly wear out are the roller, foil and tungsten lamp heaters. The roller bearings, thermistor, thermal cutout and connector are less susceptible to wear so they might be visually inspected. The problem is that stripping a fuser, exhaustively testing all the parts then rebuilding is likely to have a higher labour cost than simply assembling a fuser from new parts. At the end of the rebuild there can't be quite the certainty of a good job. Much the same consideration applies to cartridges.
Recycling is clearly the right thing to do despite the logistics problems. Some of the major printer manufacturers apparently not only ecycle fusers but are so confident of the result that they no longer make a distinction between their own new-made and recycled products. If they are recycling there genuinely seems to be no difference in the quality. (But we'd love to know the statistics)
We generally suggest that end users with a single printer that must work reliably stick to new fusers. Refurbished fusers are somewhat less reliable. Often the defects in refurbished fusers are easily spotted and fixed by technicians so they are good value if you are confident about your diagnostic skills and not too bothered if there is a delay fixing the printer.
If you aren't confident of your own diagnostic skills, are already using efurbished toner cartridges and won't be able to distinguish between a truly faulty fuser, bad installation, a bad cartridge or a wrong printer setting then stick to buying new fusers. New fusers are very arely faulty.
Alternative Fusers: |
Nupro manufactures new printer parts aiming to equal or better the manufacturers own. Nupro products should be attractive where the manufacturers own spares are high priced or unavailable. Since the components are new there aren't the quality issues that can afflict ecycled products.
Nupro parts mostly work just like the manufacturer original. There is some potential for the Nupro part to be marginally different in things like heater resistance or thermistor value and this might cause issues. Normally the problem will be cleared by things like upgrading the printer firmware - fixes which might be needed with manufacturers original parts as well.
There is a potential conflict between Nupro and the printer manufacturer. It's no good ringing the manufacturer support line and saying a recycled or Nupro fuser won't work - you can probably guess their reply!
At the moment the alternative sources for fusers are few and far between. Counterfeiters may be making inkjet and sometimes even laser printer cartridges but they don't seem to be tackling laser printer fusers. Its a small industry, there are only a couple of dozen players in each market and people know what their competitors are doing. Other sources for fusers are Bannerbridge, Zebra and Alternative Copier Company.
Parts Price and Availability: |
Fusers are the most significant spares sold for printers. Cartridges, drums and waste bottles count as consumables, which might strike the man in the street as not really different. In the computer trade there is a presumption that cartridges will be distributed alongside paper and installed by users. Manufacturer's see cartridges as an opportunity to make a profit, they actively want to sell them, even for old printers.
Spares are distributed alongside motors and electronic parts, these parts are usually installed by engineers. It isn't clear whether manufacturers want to sell fusers and there might be a few reasons why they don't.
Fusers usually last a long time so users aren't familiar with the faults they might give. That tends to result in technical support calls where they discover that fitting a new fuser out of warranty is likely to be costly and could even require the additional expense of an engineer call-out. Conversations are likely to go along the lines of "this printer had defective workmanship and I want something done about it" when actually the printer has done 100,000 pages and that is what the fuser was rated for. The manufacturer didn't say that the printer would last that long before needing a fuser and the customer didn't ask.
The price of a fuser varies mainly by manufacturer, then with the size, complexity and frankly with the price of the printer. A fuser bought as a spare typically costs a quarter to half the price of an equivalent new printer but sometimes more.
The price of fusers has little to do with the price of mass manufacturing the part itself; it's partly a matter of the logistics costs of moving special parts and after that it is pretty largely a matter of how the manufacturer wants to play the market. Do they want to treat fuser failure as being:
- the end of the printers economic life and make fusers hard to get, hard to change and unaffordable
- or just another incident in the life of a machine that can print millions of pages
Some manufactures don't seem to want printers repaired. This wouldn't entirely be surprising, it is probably more profitable to ship a new printer than to deal with the logistics and support problems raised by spares.
Manufacturer power over parts price and availability can pose several problems.
Firstly there is the problem of finding the correct part. Manufacturers have been known to list some of the major parts in sales literature but that is surprisingly uncommon. Encouraging customers to look at parts costs might seem like a bad idea to marketing departments. It is usually left unclear whether the cost of replacing the fuser is included in the per-page prices quoted for laser printers. Not surprisingly it generally appears not to be; the manufacturer thinks (or hopes) users will throw the printer out when it needs a new fuser and write of it's purchase price.
User manuals are often obtainable online and the information needed is sometimes there. Note that user manual parts numbers are often out of date.
Service manuals usually do list all the parts including the fusers, again they can be out of date. Some service manuals are available online these days. Manufacturers seem keen to keep service information to themselves and their authorized service providers - which is a problem to the numerous self-maintainers.
HP. Lexmark and Konica Minolta make a lot of spares information available online.
There are lots of online parts suppliers listing parts as well. Most give no information beyond that provided in the manufacturers lists. We do try to.
Prices:
All printers are repairable if the parts are available at a reasonable price.When you buy a printer there is an enormous choice of makers - Brother, Canon, Dell, Epson, HP, Lexmark, Konica, Kyocera, OKI etc. When you have a printer there some choice of supplier for consumables - ecyclers and clone cartridge makers. For accessories like trays there is usually little choice although there are (or have been) companies making extra trays and duplex units.
There is rarely a choice about spares; only the manufacturer has them, at least where fusers are concerned. There may be some choice about ollers - most HP print engines were made by Canon for instance and there is a lot of commonality in parts. It is possible that a fuser from another printer with the same engine will fit but it might not work. It is possible for two fusers to look the same but have different heaters and thermal sensors. Changes in temperature value to match the toner selected by the manufacturer often mean fusers cannot be swapped and work correctly. A low temperature toner can make a horrible mess of a fuser it wasn't intended for.
Buying a Fuser: |
The outline of how a fuser works above should make clear what kind of defects a faulty fuser will produce and what error messages it might give. When a printer shows an error message or a fuser defect there is a choice between buying a new fuser and buying a new printer.
Most fusers are bought online. There are simply too many varieties of fuser for most computer shops or repair operations to keep many on the shelves or if they do it will be half a dozen types. That goes for online sites as well, to our knowledge about half a dozen of them actually have a warehouse behind the offices that runs the site but quite often they do not have all the stock they advertise there. The logistics of the IT industry are quite complicated, the costs of holding spares can be very high with up to 60% of them going to waste. (We used to stock fusers, currently we have many of the rollers but just a few fusers. We found it was more economical and flexible to get distributors to ship direct to customers rather than keeping them ourselves and that is reflected in pricing).
The most common fusers are shipped overnight from national warehouses. Less common devices arrive on a 2-3 day basis from Netherlands and Germany. Some fusers seem to come from the manufacturers single global stock or perhaps there is a stock of cores and the fuser is made to order. This explains the 7-10 day wait for less common fusers.
The point has been made that there are lots of different designs of fusers - at least as many as there are printer designs. When a manufacturer changes the design of a printer engine to make it faster they almost always change the fuser design. Before ordering a new fuser be sure to get the right model. Fusers are engineering spares rather than consumer items and suppliers will not accept returns once they have been unpacked and will only accept genuinely defective items once they have been used. Look twice; order the right fuser.
When you receive the fuser check the delivery note before opening the box. If there is a discrepancy check it out. Is the item delivered what was ordered? If the delivered item is wrong suppliers will swap it, but if it is right, you are buying for commercial purposes and specified the wrong thing they do not have to. If you get it wrong make it difficult for them to say no to a return by not even taking it out of the packing.
When you are convinced you have the right item take it out of the box. Notice how it was packed. HP often make the foam insets as a sort of cradle. The fuser only fits one way and this more or less ensures that the fuser in the box is what it said on the box. In the unlikely event you do have to send it back its good to know how to re-pack it.
Visually inspect the fuser for any issues. - cracked plastic, bent metal, the heating lamp having fallen out of it's housing. look for the paper exit sensor (there usually is one) and make sure it is unbroken and moves freely. Some fusers also have a paper entry sensor which should be checked as well.
Generally a new fuser's cogs will look pristine wheras a refurbished fusers cogs will not be quite so clean. People sometimes remark that the metalwork of a fuser is scuffed and it looks as though it has been used. The look of the metalwork isn't likely to mean much - marks are likely just from manufacturing and testing. Fusers are made as spares, not as consumer items so the metal isn't bright plated to look good.
Another vital check is that the fuser looks like the one you are about to eplace. Different coloured plastics aren't likely to be significant and there are progressive refinements in design but overall the old and new fusers should correspond.
Fitting a Fuser: |
There are hundreds of printer designs and it is obviously impossible to give a guide to them all here. It is possible to give some general guidelines. We have a few specific guides here.
Always turn the printer off and disconnect the power before working on a fuser. Off switches sometimes don't entirely cut the power to the printer. Fusers are almost always directly connected to mains power and whilst designs rarely expose the user to handling live terminals they aren't all guaranteed user friendly and safe.
Some recent printers make changing the fuser as easy as changing a toner cartridge. Fusers are almost always in the rear of the printer at the opposite end to the paper feed process. It can be a matter of just otating a couple of levers and the fuser slides out. It's usually a fairly large and heavy object but nothing extraordinary. Big fast colour A3 printers do have correspondingly big heavy fusers.
The older style of fuser isn't as user friendly but isn't too difficult to fit. There are generally a couple of printer covers to remove to get at the fuser. It is obviously particularly important to disconnect the power to avoid any risk of electrocution. The Kyocera FS1500 has the power distribution board right where an engineer would naturally reach to move the printer around - ouch! Most fusers are held in place by four screws - sometimes they are thumbscrews and sometimes a long-handled screwdriver is needed to each. Use a magnetised screwdriver and take care - the main-motor cog chain is near the fuser and anything dropped into it will do a great deal of damage when the machine is turned on.
Fusers don't generally come with a set of instructions on how to change them because they are regarded as engineering items. There aren't usually any instructions in the user manual either; they are in the service manual. Service diagrams are quite widely available online - several US and one German spares sites are providing them. Full service manuals are often available online for a small charge or (less legitimately?) on Ebay. Manufacturers policies on the distribution of service manuals seem to be based on the computer industry as it was 20 years ago in the days when laser printers cost thousands of pounds, everyone had a service contract and self-maintaining IT departments were unknown. They could just make them freely available as PDFs but presumably some of their "business partner" resellers would object.
A gauge of how easy it will be to change a fuser is usually to remove the old one. The printer isn't going to work until its been replaced after all. If you find it too daunting then call a service engineer.
The mechanical engagement for the cogs is usually at one end of a fuser and the electrical connectors at the other so the fuser will probably need a bit of jiggling to lift out. Fitting a new fuser might take similar actions.
Many fusers simply slide into place and a multipole connector at one end mates with one on the printer body to make the circuit. This is convenient and makes changing a fuser nearly as easy as changing a cartridge. Unfortunately it does make it difficult to "bell out" the heater (see above)
Some fusers use trailing wires to connect to the printer. Whilst this is simple it is a common cause of problems. The connectors for mains power and sensors are usually very different and polarised in some way so that it's almost impossible to get them the wrong way round. The main problems is that even experienced technicians sometimes trap wires against the printer metalwork. This doesn't always give an instantaneous problem, it takes a few days for the pressure or cutting edge to work through the insulation until the wires touch metal and a fault develops. At this point the technician says the new fuser has failed - and appears able to demonstrate it by changing the fuser and having the printer work. The problems are that the fuser wasn't faulty so if it is returned it is still chargeable - and if the fuser wires are damaged it is now useless for resale. Even worse, if the printer side of the wires were damaged then the problem is still there and waiting to create some random error. Damaged wires need inspecting and if it is appropriate binding up with self-amalgamating tape.
Problems After Changing A Fuser
After changing a fuser users sometimes find that print becomes faint, smudged or blotchy. They immediately think the fuser must be a "dud". I don't think there are backstreet workshops in Lahore making counterfeit fusers - although there are counterfeit cartridges on the market. If there is an issue with counterfeiting HP should be able to tell by the serial numbers.In practice it is rare for new fusers to have a defect at manufacture and they are packaged so that damage in transit would most likely be visible on the box.
Problems like faded or dirty print are not likely to be caused by the new fuser. Fusers don't determine how much toner the print cartridge(s) apply to the page, they merely adhere toner. So why do problems sometimes happen?
Fusers are large objects and changing them changes other things in the printer. A lot of engineers clean the printer out and change the feed ollers and possibly the the transfer roller as well when they change a fuser. The printer works using various electrostatic charges and a big change, dust, dirt and contacts not properly made can have dramatic effects. Getting the printer back towards it's original state of cleanliness usually corrects problems. If you are changing the fuser allow a bit of extra time to clean the printer.
It is not impossible for a new fuser to induce a fault but for the fuser not to be faulty. New fusers also change the qualities of the fuser roller or foil and this can bring to the fore any changes that have been made to compensate for the decaying qualities of the old one. It is quite common to find that users have turned the fuser temperature up (often a setting in the printer menus) or changed the media type to heavy (which has a similar effect). The new fuser will run too hot to the point where toner sticks to the oller and echoes or ghosts of a line of print will occur down the page.
A dirty printer often gives faint print. A particular problem is paper dust on the transfer roller and one way users find to compensate is to turn the printer's darkness up. When the printer is cleaned the transfer roller works properly again and the print is now too heavy and some may stick to the fuser rollers.
Recycled cartridges can have a similar effect. If the cartridge recycler has used a marginal grade of toner then it may work in old fusers with worn non-stick surfaces but not with new ones. It is no use complaining to a printer maker (or distributor) that a new HP fuser fails to work with your recycled cartridge - they are just going to espond that it will work with HP toner. If you change the fuser and have print quality issues be prepared to try using a manufacturers original cartridge. Print quality problems usually come from the print cartridge, not from a new fuser.
An interrupt test is one way to find out whether issues are coming from the print cartridge or the fuser. To do this you have to be familiar with the noises the printer makes as it operates and note the noise that occurs just before a page emerges from the machine. Now send a configuration or self-test page, something simple anyway. Just before the noises that suggest the page is passing through the fuser and about to emerge gently open the printer's lid. The moment the lid opens the print engine will stop with the page part printed and part passing into the fuser. Look at the page going into the fuser - if it already has defects then the problem comes from something before the fuser.
It is more difficult but not impossible to do the same thing on a duplex printer. Just send two pages and wait until the second page is about to emerge.
Experience of shipping hundreds of fusers suggests manufacturers new fusers rarely give problems. With the exceptions we've noted there is one ultimate source of fusers - the printer manufacturer (or their contract assembler). Manufacturer quality control over fusers generally seems good. In the end analysis a fuser is a relatively simple object doing a fairly straight forward thing. Whilst a fuser's working is usually hidden inside the printer it is possible to analyse what might be happening and correct it.
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© Graham Huskinson 2010
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