25 YEARS OF PRINTER REPAIR KNOWLEDGE
One of the most common complaints seen on the Hewlett Packard LaserJet 4200 Series printers, which really includes the LJ 4200, 4250, 4350, and even the MFP 4345 in this case, is a loud grinding noise from the rear of the printer. All of these printers contain a pivoting gear case assembly known as a Swing Arm Assembly (HP Part Number RM1-0043-000CN). The Swing Arm Assembly meshes with the Fuser Drive gear to allow the fuser to rotate properly. This gear wears out causing a loud grinding noise. Eventually paper will start jamming in the fuser unit near the back of the printer.
The Hewlett-Packard Laserjet m600 paper tray is designed to lift the paper up to the feed roller. Sometimes the paper can become misaligned where the a page underneath the stack of paper folds around the lead edge of the paper stack. When this occurs, the printer may display a paper jam condition, but there will be no paper inside the printer.
I cannot stress enough how important the toner cartridge is to overall print quality. Anytime you're experiencing poor image quality, start with a toner replacement. Toner cartridge problems represent over half of the service calls Technicians face on a daily basis.
Don't have a spare toner? Try this trick before you purchase a new one. Run a test page and let the page feed just enough to reach the toner cartridge inside the printer, but before it gets to the fuser unit. Next, open the toner door or unplug the printer to jam the paper under the toner cartridge. Take the toner out of the printer and look at the partially printed page. Note: Be careful, the page has not passed through the fuser unit and toner is a messy powder at this stage in the print process. If the jammed page has the image defects visible, you most likely have a toner cartridge or image drum problem.
Most Hewlett Packard and Lexmark B/W Laser Printers have a single toner cartridge that contains the drum, toner and developer units. Some other models, including some Kyocera and Brother laser printers, have separate components... a drum, toner and developer unit. On those models finding the faulty component can be tricky, but its best to look for visible problems on the image drum first.
Note from the Printer Guru
So you really want to repair your own printer? Here are some simple (and not so simple) articles to help you.