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I have a HP LaserJet 4050n. The problem is that since a few days it suddenly started printing empty pages. A day or two before, I fixed the paper tray unit, but after that I could print a correct test page.

The cartidge was empty, so I replaced it with a new one, but it does not solve the problem. It prints blank pages when I try to print the configuration page, too. I cannot figure out why it stopped working, because the power contacts to the cartidge look okay to me. The drum looks very clean and it turns, which I verified using a felt tip marker.

Any help/hints how to solve the problem? I think it might be some problem with the high voltage but I'm not sure. Is there some special fuse for high voltage which might have melted and can the printer detect these things?

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Have you checked/replaced the transfer kit? – Justin Pearce Apr 26 '12 at 19:00

If the printer prints blank pages (including internal ones like the config page) then it means either a faulty or empty cartridge, or some internal hardware problem. That could mean bad contacts somewhere or, in the worst case, a dead laser or high voltage unit.

The funny thing is that the printer should recognise those problems, and refuse to power up - so you'd never be able to print that config page. Admittedly, the 4050 is a bit old, but I'd be surprised if it did not have those smarts.

Have a look to see if something (like a piece of paper) could be obstructing the laser beam. If you remove the cartridge, the laser window will be in the printer facing the the drum when the cartridge is installed. Then again, printers detect stuck paper and flag a paper jam, again preventing you from printing.

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I tried the printing unit with a self-test button at the side and it worked. The button bypasses the control unit (where the OS resides and the JetDirect card is connected to) completely. So the problem seems to be somewhere between control and printing unit – user3001 Nov 14 '13 at 8:33
    
As the problem seems to be in the controller, you can try to do a factory reset on it. Turn it on while holding GO. Release it when the printer says INITIALIZING. When OFFLINE appears, press GO and it will be reset. – hdhondt Nov 15 '13 at 9:41

If the left hand cover arm end is broken it will not open the lazer shutter. The end of the arm has a little pin stub that when you open the cover when replacing a cartridge closes the shutter. We have had many of these machine and still use them. Two of them had a broken left arm end and one stopped working. Finally after taking off the top panel and looking, looking, thinking what the problem was and finally thought it was the power supply or lazer itself a bystander said "what is this little plastic piece over here", pointing to the left side of the lazer unit. OMG!! its part of the arm that actuates the lazer shutter. Machine fixed with a little plastic glue!!

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