Laser Printer Faults - White Page.

Some documents do contain white pages, typically as separators between the title page and body. Chapters conventionally begin on an odd-numbered page. Quite a few documents intended for print on offset litho machines will contain several blank pages at the end because the A0 or web feed to the machine has to be fully occupied; if the same document is printed on a laser printer there will be some blank pages.

In electronic documents like PDFs, chapters are usually arranged so that a new chapter starts on the front of a sheet - not the reverse side.

Blank pages are also used to allow a double-page spread in some positions. For instance a circuit diagram may need a double-sided spread so that a preceding page might be left blank.

More irritatingly many web pages print a blank page after the document - (the defect might be the page; more likely it is the browser or the print driver). There are some software solutions that promise to fix this.

Blank Pages as a Fault

If the printer definitely should be printing material and isn't:

• Most likely a sealing tape is still in the print cartridge. Check the cartridge - the tapes usually have bright orange or green tabs to help identify and remove them but they do get forgotten. Manufacturers obviously take some care to make sure tapes don't break by accident but it can happen.

Try a printer configuration or self-test page to see if the printer can work normally.

Other possibilities are:

• Completely inappropriate media
• Blocked laser path or an alignment problem (if it's write black).
• The laser has failed and can't write
• Failure of a transfer voltage.
• Completely exhausted cartridge.

Inappropriate media

The laser printing process relies on electrostatic charges to work. Before trying to print on new media it is best to check the user manual. Watch out for things like melting points and adhesives. Using the wrong kind of transparency can wreck a laser printer fuser and costs a great deal to replace (manufacturers will not cover such accidents under warranty).

Some media may be capable of passing through the printer but things like labels with a metallised surface, for instance, might be incapable of dealing with the electrostatic fields.

Failed Laser.

Printers usually have a beam opto-detector that the polygon mirror will sweep the beam across at the beginning of its travel. The primary purpose is timing but if it fails to happen, the printer can normally detect that the beam has failed altogether. Originally Laser Diodes were subject to catastrophic optical damage; imperfections in the mirrors would lead to localised heating, worsening the imperfection and destroying the device. Recent lasers do not often fail outright although they do run fairly hot and it can happen.

Laser diodes do lose power over time. The printer may compensate for this by altering the laser drive voltage or the voltages in the electrophotographic circuits.

Blocked laser path.

Caution! The beam in a laser printer is sufficiently powerful to damage human eyesight, so only test the shutters when the printer is off. Incidentally, the laser is almost invariably infra-red so there is nothing attractive to see with the beam on.

Laser paths on mono machines are normally down onto the cartridge - a narrow slit in the cartridge over the drum lets the laser scanning beam in. Some cartridges have a shutter over the beam entrance but some modern designs don't seem to bother with this. If there is a shutter make sure it can move.

The laser scanner assembly is usually part-triangular in shape (the laser and scanner are at one end, followed by some optics and a mirror finally deflects the beam towards the photoconductor. By examining the cartridge it should be possible to spot the laser scanner exit.

There will usually be a shutter over the laser exits themselves so that they are only opened when a cartridge is in place and / or the lid is closed. With power off check that the shutter is able to move.

Because the beam slits are quite narrow it is not unknown for paper swarf to get into them. Printer designers seem curiously relaxed about dust getting into the optics - it wouldn't take much effort to make a sealed enclosure but they don't bother. Normally this sort of problem will result in fading or irregularities, not an outright white page.

If a printer has been dropped then the lasers may be out of alignment. Normally there will be some tell-tale damage to plastic. Realignment might be covered in a service manual but most modern printers use assemblies aligned in the factory and not intended to be done elsewhere - it would need infra-red camera detectors and suchlike.

Transfer Voltage.

Complete failure of a transfer voltage might produce a white page. The inverters that produce the high voltages do fail, but not frequently. Look for damage to a connector before concluding that a new high voltage power supply is the solution.

Exhausted Cartridge.

Cartridges normally give faded print before they fail to print at all. There will come a point where the cartridge just doesn't print. Printers will normally detect and report this.

• Printers may rely on communication with a cartridge chip to warn of the toner condition so remanufactured and compatible cartridges may not be able to warn of exhaustion adequately. Print will fade when a cartridge is used.
• Some users press on regardless to empty the cartridge.

Although cartridges are sealed, it is usually possible to feel some toner shifting inside if they are shaken a bit.

Stop Test.

One way to identify whether the problem is one of transfer or media or earlier in the process is to try a "stop test".

Set the printer in motion printing something like the self-test page or anything else with plenty of print. Wait until the page seems to be about halfway under the print station - it will usually be one or two seconds after the page sets off. At this point open the lid or cartridge door. The safety interlock will shut down the motors and laser.

Take the cartridge out. The page in the print station should be about half-printed, look at the page and if the problem is blank pages then it should be blank too. It may be partly in the fuser in which case the back may need to be opened to open the fuser grips and remove it.

Examine the print cartridge or OPC drum. Since the printer was interrupted whilst printing, if the transfer station was the problem there should be writing on the drum. If there is writing on the drum but none is transferring to the page that suggests a problem with the transfer roller, its voltage connection or high voltage circuit. Look for toner contamination on a connector or anything else that could interrupt the transfer voltage.

If there is no sign of writing on the drum then either the pre-charge conditioning, the laser, a shutter or the developer isn't working.

Other Issues.

Colour laser printers often have a mechanism to disengage the colour cartridges so that they cannot print. In the Laserjet 3600 etc, this mechanism can break so that the colours go missing. Many printers have specific issues of this sort. There are too many issues to list them at present.