"More and more I get HP Laserjet IIIP printers here with all the same problem: 13 Paper jam. Every time I look at the driving-mechanism and move it with my hand, but it all seems to work fine. I suspect there's a common cause to all this. I think it's got something to do with the electromagnet in the tray, but I'm not sure."
(From: Frank Reid (firstname.lastname@example.org).)
If the paper is getting crunched accordion-style, the 'drum-drive clutch' is probably broken. It's a couple of small white gears inside the right-side cover of the machine. The plastic tends to crack in a ring, separating the gear from the shaft. To confirm, mark the green drum in the toner cartridge: If it doesn't turn, then the clutch is surely at fault. Apple "Personal Laser Writer" and some other brands use the same print-engine.
If the machine won't pick up paper at all but the pickup rollers are good, look for a bent piece of metal preventing movement of the bar that raises the stack of paper just prior to pickup.
A third possibility is stripped plastic gears on the fuser assembly.
(From: Lars Arvidsson (email@example.com).)
My guess is the paper intake rubber reel, you see it if you pull out the paper tray. It gets old and dry, and it needs to be sticky to get a grip on the sheet. It gets worse at dry weather, cold and dry. Try to clean it with alcohol, then coat it with some balsam turpentine (don't know if this is the right translation, it's a liquid used for diluting artist oil paint).
Allow it to be absorbed for a few hours, then wipe of the excess. The reel is sticky again...or just replace it - but that's no fun. ;-)
(From: Rick Norton (RKNORTON@worldnet.att.net).)
I repaired an HPII with a similar problem using automotive belt dressing on the rubber pickup surfaces. Spray a small amount on a rag and wipe on surface. Allow to dry for 15 minutes. The printer has been working for 3 years without a problem.
(From: Dr. John Betts (Dr@browser.demon.co.uk).)
Don't ignore a more mundane cause - that paper is stuck inside the fuser, particularly if someone has used inferior grade labels.