Printer Faults - Horizontal White Stripes

Most printers produce the page as a raster vertically - that is the page starts writing with a top line between 1/50th mm and 1/10th mm thick and then repeats that down the page at 300, 600 or 1200 lines per inch.

Note that A3 laser printers very often produce A4 pages wide-side on, this gives them a potential print speed advantage because they only have to print 8 inches of paper for each page - but of course the whole print process is turned on its side.

Normally all the rollers and the processes they undertake are pagewidth. To produce a horizontal mark one of the rollers would itself have to have aquired such a mark but the direction they are turning in would tend to produce vertical marks - and they are indeed more common

The most likely source of a horizontal problem is the print cartridge - particularly the OPC.If the stripes have indistinct edges then the drum may have been exposed to light. Check against the regular defects chart for the printer in the service manual if possible.

Any roller with contamination across it rather than around it could in principle cause this fault - but they are mostly in the print cartridge so not likely to be contaminated and the fault should shift with the cartridge

Another possibility is the transfer roller

The transfer roller could conceivably be contaminated along the top (dust ? toner dumped from the cartridge? ). It might also have been handled. There are a few reports of an incomaptability between transfer roller and OPC material causing a reaction.

The fuser isn't likely to do this. Perhaps if the surface of the hot roller or foil was contaminated by glue from an envelope it might subsequently produce a few pages like this before it started producing darker marks of baked on toner as well.

Fuser pressure rollers are sometimes distorted when they have been stored with the pressure springs engaged and in those circumstances the uneven tug of the fuser might create a pattern. It would be more likely to be vertical distortion than missing areas.