If you get a grinding and knocking noise from a HP LaserJet 4250 or 4350, the problem is the swing plate assembly and / or fuser. The swing plate assembly is a metal bracket with two plastic gears on it and drives the fuser.
The problem is that the teeth on one or both of the gears wear. You might also find that the plastic clip that holds the fuser in place cracks. The new swing plate assembly is modified to reduce the wear on the gears. It is also supplied with a modified two part spring loaded fuser gear. The new fusers are also modified with a metal insert inside one of the plastic clips to stop it from breaking.
The good news is that HP will send an engineer out to repair it free of charge even if it is out of warranty. Tell them it is making a grinding noise from the back of the printer and that you have tried reseating the fuser. If they tell you the printer is out of warranty, remind them that there is a service note that covers this fault.
Update
As of January 1st 2010, HP are no longer repairing this fault free of charge so you will have to do it yourself or take your printer to someone who can do it.
If you decide to repair the printer yourself, there’s a right and wrong way to do it.
The one gear can be changed very quickly by removing the formatter cover, formatter assembly, rear door, and fuser. Behind the formatter, you will find a black screw. After removing this screw, the gear can be removed from the back of the printer.
The problem with doing it this way is the printer will still be noisy if the other gear that you can’t see is worn.
The best, and correct, way to do it is to replace the whole swing plate assembly which requires removing the power supply board and is quite a lengthy process.
Briefly, what you have to do is; remove the top cover, both side covers, rear door, and fuser. Disconnect the cables from the power supply board at the dc controller. Remove six screws and an earthing screw holding the power supply board in. Remove the power supply board from the back of the printer.
The swing plate assembly can then removed from inside the printer by removing the three black screws. These are hard to get to and can be tight and are easy to round off. The swing plate is also tricky to get in and out of the printer.
If you get a genuine HP part, it should already have some grease on it. If you get a cheap compatable part, you might need to grease it yourself.
When you tighten the screws holding the power supply in place, pull upwards on the power supply. This moves the fuser gear closer to the swing plate gear.
Fit the new fuser gear supplied in the kit onto the fuser. Don’t forget to check the plastic retaining clips on the fuser. If they are broken, the fuser will need to be replaced.
Hopefully, your printer should now work, and should be a lot quieter.
