Monday, 11 March 2013

HP 2600n Colour Laser Printer

Magenta fade and poor printing

I have a HP 2600n colour laser printer, which I have had for around 5 years and it has proven to be a very reliable printer. However recently we noticed that the colour printing quality was not as good as it used to be. To start investigating I printed a demo page (press left and right arrow together).

The demo page showed that there were slight problems with the alignment of the four different coloured toners. It also shows, but is not as easy to spot, a problem with the magenta toner. You think that the magenta is OK as the soldier’s tunic is red so you assume that the magenta is working fine.

To further prove that there was a problem I went to this page from Refresh Cartridges  and printed out the test page for colour laser printers. What that showed was that the magenta was fading on the left of the page.

Doing a quick search I found that this is a very common fault with this printer and the other printers that are based on the same workings such as the HP 2605 and HP 1600 and the Canon LBP5000. The problem is due to dust on one of the mirrors that the laser beam is reflected off on its way to the toner cartridge.

The optical box that contains the lasers, lenses and mirrors is not sealed against ingress of dust, and as the printer has fans to cool the internal workings of the printer, the result is that the fans suck dust in from outside the printer and deposit it inside the printer. If I was a cynical person I might think that the printer was specifically designed that way to try and get people to buy a new printer, after buying a new magenta cartridge that didn't fix the fading problem!

The optical box looks complicated, and it is, but it’s not as complicated as it seems on first glance. There is basically one set of mirrors and lenses that have been copied another three times to give a set of lasers, lenses and mirrors for each of the four different colours.

Each one of the four different coloured sections is made up of the following basic components:
  1. Laser – covered by shutter in picture
  2. Lens
  3. Rotating mirror – only one per pair of colours
  4. Lens
  5. Mirror – this is where most of the dust will be
  6. Compensating lens
  7. Calibration detector – only one per pair of detectors

The laser beam is emitted from the laser through the lens which focuses the beam on to the rotating mirror which then reflects the beam through the next lens and onto the mirror. The beam is the reflected through the compensating lens and onward to the toner cartridge. If you look carefully at the lens before the rotating mirror, you will see that there are actually three lenses moulded in to the plastic. Two of them are the lens that the two laser beams pass through before hitting the rotating mirror. The third one focuses the beam on to the calibration detector which is located back on the pcb.
All the lenses are made of plastic and care must be taken in cleaning them as they are easily scratched. The mirrors are also delicate as the reflective surface is on top of the glass and not behind the glass in a normal mirror. The magenta and yellow mirrors are particularly susceptible because the face upwards and any dust floating down will settle on them.

I came across an excellent site that takes you through the fix step by step. I am not going to repeat the steps but just going to point you towards the excellent site.

I recommend that you follow the instructions on the above site and then read the extra problems that I overcame.

After carefully cleaning the optic box and making sure that the box was sitting correctly inside the printer, I printed out the Self-Test / Configuration page from the printer. 

The good news was the magenta was OK all across the page; the bad news was the four colours were completely out of alignment.

I tried calibrating the printer, and although that changed the alignment of the colours it still was not correct. After more searching on line I tried a “Super NVRAM reset” by holding both arrow keys down whilst turning on the printer. According to all the warnings I found on line this reset clears all the non-volatile memory in the printer which could also wipe the record of the number of pages that have been printed. In my case the page count was not reset.

After doing the NVram reset the alignment was back as it should be hooray!

The print demo page also looks a lot better, there are reds all across the picture, the colours are aligned and you can even read the name on the side of the train!

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