January 2006 Featured Technical Article

The HP LaserJet 4200/4300 Series Swing Plate Assembly
Playing Hard to Get

There’s not much to an HP LaserJet 4200/4300 series swing plate assembly (part number RM1-0043) – just a couple pieces of metal, a few gears and a spring (Figure 1) – but like most parts inside a laser printer, if it fails to function correctly the printer will let you know about it. This article will outline those ways, as well as give detailed instructions on how to replace the swing plate assembly, should you need to.

A Simple Purpose
The purpose of the swing plate assembly is to engage the main drive with the fuser, causing the fuser to turn. One of the gears on the swing plate assembly engages with a 40-tooth gear on the fuser (Figure 2) when the top panel is closed. If the fuser is not fully clipped into place – or if the fuser has a broken fuser clip – these gears may not engage properly. If that is the case, two things can happen:

1. Paper jam - If the gears don’t engage at all, the fuser roller will not turn. When paper reaches the fuser, a paper jam will occur.
2. Grinding noise - If the two gears engage improperly, a grinding noise can result, which can also cause damage to the fuser gear, the swing plate gear, or both.

If you experience either of these scenarios, the first thing you should do is remove the fuser and check the fuser gear, the two fuser clips (Figure 2), and the gear on the swing plate assembly for damage. You should also lift up the gear on the swing plate assembly to verify tension (Figure 3). If there is no tension, the spring on the swing plate assembly is detached, missing or broken. If that is the case, it is time to install a new swing plate assembly, since the spring by itself is not available. If there is tension and the gears and fuser clips are not damaged, reinstall the fuser. If the paper jam or grinding noise subsides, then the fuser was not seated properly in the printer. If the problem still persists, continue trouble-shooting as recommended by the manual – the swing plate assembly is not the culprit.

Figure 1 - The swing plate assembly for the HP LaserJet 4200/4300 series (part # RM1-0043).	Figure 2 - The 4200/4300 series fuser has a 40-tooth gear (red box) that engages with the swing plate assembly. Blue clips on either side of the fuser (red arrow shows right clip) secure the fuser in the printer.

If you do find damage on the fuser gear, don’t assume that you can just replace the fuser and solve the problem. It’s costly and embarrassing to install a new fuser in a customer’s printer, only to experience the same problems with that fuser due to one bad gear chewing up the other. If you see damage on the swing plate assembly gear, you’ll have to replace that also.

Playing Hard To Get
The good thing about installing a new swing plate assembly is removing it from the printer’s frame is easy – simply remove the three screws holding it in place. The hard part is all the parts you need to remove to get to it. As you’ll see in the following instructions, a good portion of the printer needs to be disassembled until you can finally get a screwdriver to the swing plate assembly. It’s for this reason that we strongly encourage you to try reseating or exchanging the fuser first, as these options take much less effort. However, you may not have an extra known good fuser on hand, and since the fuser is considerably more expensive than the swing plate assembly, taking the extra time to install a new swing plate assembly may be worth it.

Getting To The Swing Plate

1. The swing plate assembly is nestled deep inside the printer (Figure 3, red box) and requires a lot of disassembly. Follow these steps to get to it.
2. The first step in removing the swing plate assembly is to remove the rear face-up tray, toner cartridge, fusing assembly, and the left, right and top covers.
3. Remove the formatter and its cage by removing two screws (Figure 4, red arrows).
   
   

   Figure 3 - The red box shows the swing plate assembly as it is positioned within the printer.	Figure 4 - The red arrows indicate the two screws that attach the formatter and its cage to the printer.

   
   
4. After you remove two more screws labeled “M4” (Figure 5, red arrows), you should be able to slide the right tray guide (Figure 6) out by pushing in the plastic circle (Figure 5, yellow arrow).
   
   

   Figure 5 - Remove the two screws labeled “M4” (red arrows) and push the plastic circle (yellow arrow) to remove the right tray guide (Figure 6).	Figure 6 - The right tray guide.

   
   
5. Remove the switch rod (Figure 7).
6. The DC controller has several cables attached to it, but you will only be removing the two ribbon cables and the three plugs with multi-colored cables (Figure 8, red boxes). Slide these cables through the hole in the side of the printer (Figure 9) and pull them from the other side so they hang loose in the inside of the printer (Figure 10).
   
   

   Figure 7 - Remove the switch rod.	Figure 8 - The two white ribbon cables (being held) and three multi-colored cables (red boxes) must be removed from the DC controller.

   Figure 9 - Slide the cables through the hole in the side of the printer.	Figure 10 - Pull the cables so they hang loose in the inside of the printer (right, three of the five cables shown).