68kMLA Classic Interface

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HP LaserJet 4L know-how needed!
Posted by: LC_575 on 2010-11-18 19:35:27 I have been experiencing intermittent problems with my 4L. Many times, when it picks up a sheet of paper from the cassette, everything is fine until the paper hits the registration sensor (PS1), where it will stop, causing the Paper light to flash and printing to stop. However, many times the print job will finish just fine. I checked the PS1 sensor flag; it's fine, and it rotates freely. I also checked for a paper obstruction; none is present. The manual feed slot does not work at all. Use of it will always cause a Paper error. I'd like to fix this though, because I just bought a new cartridge, the print quality is good, and it should make a fine companion for any Mac. So, does anyone (who has 4L experience) know how to fix this?
Posted by: Classic Mac on 2010-11-20 14:53:11 I haven't had that problem yet. This is the site I use to keep mine up. very helpful and parts are cheep. http://www.printertechs.com/
Posted by: Unknown_K on 2010-11-20 15:11:18 Feed problems could just be rollers that need replaced. On my HP 4si many people have issues with feed rollers getting gummed up and not grabbing the paper good so you get misfeeds. Plenty of kits out there to replace them.
Posted by: LC_575 on 2010-11-20 18:30:35 I figured it out! When originally trying to solve this problem, every forum post I saw (about this very same problem - it's common with the 4L/P series) had an answer from a Taiwanese who spoke of cleaning some "sticky solenoids." Both of these solenoids featured a foam pad to reduce noise, but 17 years of use makes the pad rot away, leaving only its adhesive, which can hold back the solenoid's arm when it shouldn't be. He mentioned that there were two of them. I knew of one already: there's a solenoid that controls the main pickup roller. But the other one was lost on me, and due to his failure to speak good English I couldn't work out where this second one was or what it controlled. Exploring the service manual I discovered that it controlled the front roller - the source of the manual feed and intermittent paper cassette problems. But the manual only pointed me to a contact assembly located on the mainboard - not an actual solenoid. Then, while I had the printer apart, I noticed that this contact assembly mated (when the mainboard is installed) with another contact assembly located on the Paper Pickup Assembly, a one-piece unit of gears and the two rollers that picked up the paper. The manual, for whatever reason, doesn't address it's removal. So I figured it out myself, managed to remove it without breaking anything, and lo-and-behold, there's the second solenoid! Cleaned it, gave it some electrical tape to act as new "foam," reassembled, and test it out. It works now, manual feed and everything! If the forum would like me to write up a full directions to fix this common problem, I will certainly do.
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