Printer Faults - Toner Not Sticking to the Page

Laser printers create the image from toner powder, this is transferred to the page then made to adhere using a combination of heat and pressure in a device called the "fuser". If pages emerge with toner still in powder form or breaking away from the page then the fuser process is not working properly. That could be a simple matter of setting the fuser temperature correctly. Unfortunately it very often means a new fuser is needed.

What Fusers Do

A typical fuser has a hot roller on the top and a cold roller beneath.

The hot roller might be heated by an inductive coil or a ceramic heater. Very often the heater is a halogen lamp running down the centre of the roller, heating it from inside. The surface of the roller is coated in a non-stick material so that it will adhere as little as possible to the toner it will heat.

A slightly different design for the hot roller uses a cylindrical foil or film of non-stick material wrapped around a ceramic heater. The ceramic heater can reach temperature is seconds and the foil has very little thermal capacity so it transmits the heat quickly to the page.

The hot roller heater will ultimately fail. The printer will be able to detect this in two ways:

• Heating requires a strong current and a simple circuit can detect whether this flows - so the printer can report the error immediately.
• Heat levels are controlled by a thermostat circuit where the temperature of the roller is sensed by a thermistor and fed back to the printers engine control circuit. If the fuser doesn't come to temperature in a "reasonable" time then the printer software will report a problem

The roller or foil will ultimately fail in one of two ways:

• Non-stick properties degrade over time
• Constant stressing as the fuser turns ultimately creates a tear which quickly spreads

Failure of the roller or foil is not usually detected by the printer, instead the user will notice regular blotches or unstuck toner on pages, progressing to become a line and possibly followed by a paper jam in the fuser.

The blotches will be a specific distance apart, corresponding with the circumference of the fuser roller. Printer service manuals often give a "defects ruler" that identifies faults by their distance apart.

Low Temperature.

Pages can emerge from a printer looking surprisingly good but with the toner not adhered to the page and smearing to the touch. This isn't likely to be fuser failure because the printer's engine control clearly thinks the fuser has come to temperature. In this case its likely that the fuser is OK but the temperature settings are wrong, set for transparency but actually printing on card for instance.

Device configuration settings like fuser temperature should be available through the driver on the computer, but they might need to be set through the printer control panel. Settings to look for are:

• Media type: set the type the user manual says is appropriate to the grade of paper
• Fuser temperature: there is often an explicit ability to turn the fuser temperature up.

Fuser temperature is one of those issues where designers are conflicted between "making it easy" and "giving users control". The majority opinion seems to be that users wouldn't want to know or understand the issues so the print driver designers offer a choice of "transparency, copier paper, envelopes, light card and heavy card". In all honesty we probably wouldn't be able to guess whether we would want the roller temperature at 150°C or 220°C. But the actuality is that the fuser temperature and pressure roller tension moves.

If the media settings or fuser temperature are changed to deal with card or envelopes then change them back when needed. If the fuser temperature is too high media will be inclined to curl, there may be some print offsetting and transparencies may melt.

If the cartridge is refurbished it is possibly with an inappropriate grade of toner. Some manufacturers run the same print engine at a higher temperature and a toner intended for one purpose won't necessarily suit another. If the toner is wrong a much worse problem is where it melts too easily - this causes offsetting but it can also make a complete mess of the fuser.

Fuser Life

Fusers usually last somewhere between 50,000 and 500,000 pages. Obviously the little fusers in small laser printers tend to last a short time and the big fusers in "production printers" last a lot longer. To some extent wear is proportional to the surface area of the non-stick material. In a more expensive printer manufacturers can provide things like electronic soft-start for the heater. Usage also has an influence. Fusers have a short life with heavily printed pages because that degrades the non-stick surface. Thick papers might also be a problem, increasing "edge wear". Service manuals often give a rated life for the fuser.

Replace Fuser

Most modern printers take the rated life and build it into the printer software, prompting users for a new fuser after so many pages. The message is intended to save trouble. Replacing the fuser usually isn't compulsory - it's up to the user to decide when to do so, although clearing the message so that it isn't a constant irritation might be an issue. Don't forget to buy a new fuser. The warning message won't be that far out. When the fuser is replaced the printer might detect this and reset the message automatically - or more likely the printer will need to be put into a service mode and specifically reset.

Repairing Fusers

In principle fusers can be repaired, providing you can get the parts and summon up the patience. Hot roller fusers are fairly easy to deal with although the plastic parts have a tendency to be brittle and crack.

Film or foil based fusers are about the same with one exception: the lubricant. What prevents the foil degenerating under the stress and pressure of contact with the ceramic heater is a lubricant that both transmits heat and is smooth flowing at 150 to 200 degrees centigrade. The lubricant is usually a white paste at room temperature. Printer manufacturers don't give any specification for the lubricant; it's a secret that might have been covered by a patent. If a replacement lubricant is wrong the life of the new foil will be compromised.

Refurbished Fusers

It is much quicker to repair ten or a hundred identical fusers than to repair one or two. It is also worthwhile researching the correct lubricant and perhaps running a few printers in-house to verify that things seem to work correctly. Refurbishing fusers has emerged as a specialist job.

Compatible Fusers

Refurbishing a fuser involves making some judgement about which bits to keep and discard. Almost all of the metalwork and many of the plastics might be good. It would be preferable to make fusers out of all new components. For a few of the most popular printers where manufacturers habitually charge high prices for spares there are "compatible" fusers. However there are something over 4,000 types of laser printer out there so only quite popular models get covered in this way. It is possible for a compatible fuser to be better made than a manufacturers original, using more recent materials and techniques.

New Fusers

Manufacturers original new fusers are relied on as replacements for a failed unit. Printer manufacturers know this and set their prices and policies for spare fusers accordingly. Some manufacturers have quite reasonable prices for fusers - it's a fairly complicated part so it isn't a surprise if the cost is 20-30% of the price of a new printer.

It is rather surprising that some manufacturers think more than half the price of a new printer is a reasonable price for a fuser. Presumably they would prefer to sell a new printer. Customers, remembering this treatment, might prefer to buy a new printer from a more reasonable manufacturer.