Printer Faults - Mucky Page Rear

If this is not a duplex page then there is no print process operating on the rear of the page.

There are several possibilities.

Transfer Roller

Loose toner in the paper feed path most probably near the transfer roller. The surplus toner needs cleaning away or it will begin to interfere more seriously with the print process.

A previous page printed onto the transfer roller. Paper got to the registration station and appeared to feed properly but jammed before it got to the transfer roller. So the print process seemed to work but the toner actually went onto the roller. After a few pages this fault will largely clear - the surplus toner will have transferred around the printer a bit.

Leaking Cartridge

This cartridge (or a previous one) appears to be leaking toner slightly. Is it refurbished or refilled? If the problem is minor clean it, then check again after the printer has been in use. If loose toner has reappeared, the cartridge seal or scraper blade appears to be failing. This is a fairly common issue with refurbished or refilled cartridges.

Either way

It would be wise to run a cleaning page if the printer has that capability (see the user manual) or to clean the printer manually if it doesn't.

Fuser

Fusers can transfer material to the back of the page although it is likely there will be defects on the front as well.

A fuser has two rollers.

One roller is heated and covered in non-stick material; this roller is intended to fuse the toner powder to the page by a combination of heat and pressure from the roller below.

Some laser printers substitute a foil or film of non-stick material for the fuser. This "instant on" technology saves time and energy, the printer doesn't have to heat a metal roller through before printing commences, just spend a few seconds heating a film.

The other roller is rubberised and intended place pressure on the upper roller.

The heated roller is coated in a non-stick material such as Teflon, however such properties are not perfect. At one time it was common for the heated roller to be augmented with a pad coated in silica oil, the pad left a thin trace of silica oil on the roller so that it was very difficult for toner to stick to it.

Later fusers eliminated the silica pad (people forgot to change it, its action was erratic and there was a health concern). Instead designers substituted an element of wax in the toner- embedded in it or micro-encapsulated. The wax helps free the toner from the hot roller.

If the toner does not suit the non-stick properties of the heated roller then it will build up and transfer onto the rubber roller. The rubber roller will then transfer bits of baked toner to the rear of the page.

The fault can be spotted by looking closely at the fuser rollers or film. Both should be spotless. If both look quite mucky there may be a problem.

In some printers a cleaning page can be initiated from the control panel or driver and that might remove the problem. Otherwise the fuser can be cleaned by light brushing with a damp cotton bud or suchlike. Do not use excessive pressure or sharp objects on the fuser surfaces - damage the surface and that is the end of the fuser.

Duplex Pages

If the page did go through the duplex mechanism and only the second side ever has a problem then:

The media might not be suited to double sided printing. (a few paper types are intentionally single sided)

The media might have a problem in the circumstances. Passing through the fuser once tends to dry the paper out

Suspect residual static in the page as it goes into its second pass. There should be a static eliminator and its tips may have worn.