Printer and Photocopier Troubleshooting and Repair Collection : Guide to disassembly and reassembly of H..  
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Guide to disassembly and reassembly of HP LaserJet 4

(From: Alexandre Souza (taito@terra.com.br).)

I fell in love with this printer but this puppy got some Coke in her fuser and messed things a little. So I was obligated to do a complete disassembly of it, to clean up the mess and change a gear. So, here we go:

  1. Open the right lateral cover, pick it out.

  2. Take the top cover out, 2 screws on the back, one on the top, beside the little green brush. You have 2 plastic locks on front, be careful with them

  3. One plastic lock on top, and you take the left panel out

  4. On the back of the printer, take the big panel out - you have the plastic hinge besides the parallel and serial connectors (best done than said) and one small "lock" on the right pin of the door (the power supply side). Take the lock out, and slide the plastic door out the printer.

  5. 2 more plastic locks, and you take the small front panel (where you put cartridges) out. The only remaining panel is the MP tray, that I didn't needed to take out.

  6. Take the formatter door out. You have a small plastic pin on the middle of the hinge of it, push it and slide the door out.

  7. Take the formatter out. You will have 2 screws on the left, behind the formatter door hinge, one or 2 screws on the top, one in the right.

  8. You are seeing the main motor. 4 exposed screws, and it is out. Take GREAT care with a hole below the left screws, if you don'ts close it (and open before using the printer) one of the left screws ALWAYS falls by this hole on the power supply. And you don'ts want it, want you?

  9. Behind the motor board, you will find 2 screws, it frees the main gear unit. This is the most fantastic thing I've ever seen - 2 screws and all the gears, inside a module, come out. I LOVE HP! :oD

  10. Behind the printer, take 2 screws on the base of the fuser assembly, take it out, push up and back the fuser assembly.

  11. 2 screws on the printer connectors, let you take out the cooler fan on top of it. It also has a small plastic lock on the left side of it

  12. Take the black ventilation colum out. This is divided in 2 parts. Take care. Take the ventilation grid on the bottom of it, and clean it thoroughly.

  13. 2 plastic locks on the BACK of the assembly that transports the paper to the top of the printer (sorry, don't know the HP name) and it is free.

To disassemble the fuser:

  1. take the FRONT plastic part out. Note there are 4 plastic locks on the front, and another one on the lower right, besides a gear.

  2. Unconnect a lug terminal on the bottom of it. Take GREAT care, this is the wire that comes from the lamp.

  3. Free all the wires from their locks, and take the two screws of the frontal thermistor (the bigger one) on the top of the fuser. Also, unconnect the small 2 wires with a connector on lower left.

  4. Unscrew the RIGHT plastic part, freeing the lamp, and with greatest care of all, unscrew the LEFT plastic part. TAKE CARE with the wires and the lamp. One wrong movement and the lamp is gone.

  5. Take the lamp out, now you can play it safe with the fuser.

  6. Take the right top and bottom gears - they are free.

  7. Take the fuser gear. You have a small lock you have to take out.

  8. Take the same lock in the left side

  9. Take out the metal cover of the fuser - you have 2 small locks between the plastic back with the green sticker (that has 2 coils that go to this cover), just pull it back and here comes your metal cover. Clean the thermistors!!! don'ts forget to change it if they are scratched, dented or damaged!!!

  10. Unscrew the fuser roller bushings from the main fuser module

  11. Find a way to make the lower rubber roller stay far from the fuser roller, and pick it out of the module. So you can pick out the black rubber roller too

  12. Clean everything with isopropyl alcohol

  13. Reassembly everything in reverse order.

This is my method of "Refurbishing" the HP4+. Note I have one with 400,000 pages printed and NO problems. The gear I changed was INTACT (as the others on the main gear module) with only 2 broken teeth caused by the roller, that was completely locked!!! It was SO Glued with coke that a small gear on the fuser, after unassembling, was completely unable to move, before taking it out with great force, and cleaning with alcohol. After that, it was free as a bird. Go figure...

Just a little fun: This one cost US$30. :o) Spent more US$40 to fix. The parts were more expensive than the printer itself he he he :o)

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