resistant

asked Apr 3, 2008 at 7:30pm
Hp HP LaserJet 4M

HP LaserJet 4M+ Incessant Paper Jams

Suddenly the HP LaserJet 4M+ is suffering from incessant "13" paper jams. It's always the same thing, over no less than ten tries (with a paper result, see below). The paper seems to be printed nearly okay, with a bar of compressed distortion at the bottom, but jams up before it gets to the fuser, as I understand the part that permanently fuses the just-deposited toner to the paper.

It needed to be done anyway, so I finally took a known good replacement fuser unit from a spare parts unit and put it into the working laser printer. After a few tries in which no paper at all was put through and the same paper jam error oddly enough appeared, it went back to the previous pattern of printed sheets that simply didn't reach the fuser unit.

I'm not certain what to check now. Do some rollers or such need to be replaced? Do paper sensors to be checked for obstructions? I did look around inside the case, but in my ignorance didn't see anything special. Nothing seems out of place or broken, although I did find and remove a small piece of wadded up paper that was apparently from a long-ago paper jam of a different kind.
Pull out the fuser and look at the white (probably yellowed) gear that drives it. If it's missing teeth http://www.fixyourownprinter.com/kits/hp/K21
by moe on Apr 3, 2008 at 10:06pm Add comment
Aha! There's a badly yellowed gear with many broken teeth. I'm surprised it worked at all previously. I do have in the spare parts unit what seems to be a corresponding (black) gear, with the usual (white) other larger gears. Do you know how difficult it would be to remove this and place it into the working printer? It looks rather non-trivial. I'm not certain how to start. It looks as if one would have to disassemble the printer to a large degree, then pop off a metal clip carefully and slide a rod down to allow removal of an entire gear assembly. There's also the apparent possibility of bending a thick metal tab to allow removal of only the specific gear in question, but I'm not certain what will happen if I do this. I don't want to damage anything.

Is there a FAQ that explains this, or a repair manual that can be downloaded? If the worst comes to the worst, does this repair kit you mention come with printed (not video) instructions? Any tips you can offer are appreciated. :)

UPDATE: All I could find on the manufacturer's Web site was an admittedly interesting PDF on selecting paper, plus the usual drivers for Windows.

http://h20000.www2.hp.com
by resistant on Apr 4, 2008 at 7:35am Add comment
Excellent, thanks. I've downloaded the manual and found the section on removing the "gear assembly", which from the picture seems to be the relevant portion. This should be interesting. It'll be an excuse to finally put the digital camera to good use, namely, tracking what got unscrewed from what so that all the bits go back to their proper places. First, I'll take apart the spare parts unit.
by resistant on Apr 4, 2008 at 4:43pm Add comment