It started out as a simple "jam call." An HP LJ 9050 with worn feed/sep rollers... which is the first thing I replaced. Then I had a jam in the fuser unit. I opened it up and saw that the paper had caught there in the classic crinkled up accordion jam. But this generally happens when the fuser is old and worn. The toner sticks to the upper roller/sleeve, the paper sticks to the toner, and you get a jam. This fuser looked clean and relatively new.
What's more, the jam codes were all over the place. I had:
- 13.20.00 (paper present at PS2 [registration sensor] when machine is turned on)
- 13.11.06 (paper stationary at paper input assembly)
- 13.11.07 (paper present in right door)
And so on and so on. There were jams detected all over the machine in the event log.
I also noticed that the paper path test (when I was able to get it through) was way out of alignment... sometimes falling off the paper entirely, as indicated in the scanned page shown here.
The pages being out of alignment would indicate (for most black and white machines) something wrong with the registration assembly. Especially in the 90XX series. The way it's set up, the registration assembly is a huge trap for paper dust, which can mess with the sensors. Not only that, but the registration rollers get hard and slick on these machines.
The reason pages were jamming in the fuser was because the toner was getting to the very edge of the print. In printers with large fuser rollers, there's not enough curvature in the roller to separate the page from the roller... the if any toner at all is on the edge, it sticks and jams.
Replacing the registration assembly fixed the problem.