Hi,
I've got an old and up until now very reliable LaserJet 2100.
After experiencing some paper pick-up problems, I replaced the feed rollers and separation pads for the MF tray and the main tray. Pick-up from either tray seems to work fine, and always picks up a single sheet at a time.
However, when feeding from the main (bottom) tray, often (but not always), a second sheet will get fed into the printer AFTER the first sheet has been picked up and fed through (i.e., the end of the page has entered the printer). It's almost like I'm printing a multiple-page job, even though it's only a single page (i.e., regular test page). The first page exits the printer normally, and then the printer stops (paper jam error) with an inch or so of the second sheet sticking out of the exit slot.
With the covers off, I can see that the solenoid is engaging to let the feed roller turn to bring in the first page, but often remains engaged a bit too long, so a second sheet gets picked up *after* the first sheet is completely picked up.
The service manual glazes over how the various signals from the paper sensors are used (or for that matter, even where they are located), so I'm somewhat lost as to how to troubleshoot this further.
Any ideas?