Wednesday, May 4, 2011

Hewlett-Packard LaserJet 5N Repair

Hi there,

here's another repair story. Just bought a good old HP LaserJet 5N from eBay for 25 EUR (+ 20 EUR shipment) which was said to be defective without any detail.
As I own a LaserJet 5N already, I thought that in the worst case I could use the eBay item as a spare part source. As it turned out, it performs even better than the one that I already had.



Defect analysis

The unit powered on and didn't show any service or error IDs, everything fine so far. I also noticed it was unexpectedly clean inside as well as outside.
After putting a toner cartridge and some paper in, the problem became obvious: no matter whether I used the sheet feeder (#1) or the paper tray (#2), a paper jam would be indicated before the page even reached the developer unit.
As I have disassembled my 5N a few times already, it didn't take long until it was dismantled for a closer look.
There are lots of web sites (+ the service manual) describing the disassembly, so to save your time, the first picture was taken at the point where all plastic covers (top, left, right) were already removed:

After all plastic is gone, four screws have to be removed on the front side of the printer, plus the wires you can see on the right:


Also remove these three screws on the left side:


After that, the feeder assembly can be pulled out (pull to the front). The side view gives a slighe idea of its complexity:


As far as I could see, no gears were broken but there is something that must block paper sheets on the left side as the first samples indicate:



Spotting the blockage

As paper goes through the feeder, it is guided by plastic paths, one of which is shown in the following picture (the large picture shows what you see when you turn the unit 90 degrees counterclockwise):

Paper guidance on the "gears" side of the feeder assembly
To get a better view of the plastic guidance paths, the white roller and spring (in the center of the previous image) are removed. This is quite tricky as the roller is locked with two "hooks" that lock in the groove on the spindle you can see in the center of the following picture:



Now it was a little easier to see what blocks the paper here. A small piece of paper and a bent piece of metal became visible:

 
A side view discovers that a staple was caught in this place! Argh. So someone thought the LaserJet 5N is capable of printing on paper sheets stapled together? Epic fail...


I love the serviceability of the HP LaserJet 5N, nonetheless this is one of the least reachable places in the whole device. It took some time and patience to get the staple out of there, but eventually the sheet feeder would work again!

Repairing the tray #2 feed

The next issue is the lower paper tray which didn't forward paper sheets into the printer. This is a classic issue but it's easy to solve (as long as no mechanical parts are worn or defective). Remove the paper tray and gently turn the printer so it sits on its left side (make sure you remove the toner cartridge first to avoid toner spill). This is what you see:


The roller indicated is the one responsible for moving the paper sheet atop the stack in tray #2 to the tray input feed rollers. The rubber wears over time and accumulates dust which both reduce its ability to get a proper hold on the paper sheet. Therefore, this part should be the first you check when paper jams occur from tray #2. It can easily be removed by pushing together the pins that stick out of the roller and simultaneously pulling the roller away from its spindle:


I recommend washing the roller with warm water first to remove dust, then treating it with medical alcohol (isopropyl) to remove dirt and refresh the rubber surface. Be sure the roller is dry before inserting it. Mind the "idle" position as shown in the photos and push it back on the spindle until it locks.

That's it for now. There is still an issue with thicker paper sheets which jam in the output feeder, but I'll have to come back to that later - no time :(

Hope you enjoyed this post!
Have a nice day.

Joe

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