HP 4L paper jam problem, not due to sticking solenoids or worn rollers

[anonanon]

I have a Hewlett Packard 4L printer that’s suddenly developed a frequent paper jam problem.

The printer is of course about 20 years old, but it has seen only very light use.  I bought it secondhand three years ago.  Its first owner had used it very little, and I have printed about 13,000 pages on it.

The D-Roller and registration roller look like new, with no cracking or wear.

About two years ago, it developed a paper jamming problem that fit the profile of sticking solenoids due to residual adhesive.  I disassembled the printer, cleaned the surfaces of both solenoids, put it back together, and had no problems with paper jams since then, until about a month ago.

Here is the way it is jamming:

If I try to print a multiple page job, usually (though not always), the printer will jam with the first page about 2/3 printed and the second page just being taken up out of the tray.

If I try to print a one page job from the tray, usually (though not always) it will print fine.

If I manually feed the paper one page at a time, waiting for the previous page to be delivered to the output tray on top, then it never jams.

I initially thought the problem was due to paper that had gotten slightly curled in storage somehow.  But when I got some new, very flat paper, it jammed the same way.

I have cleaned the D Roller and the registration roller, with no effect on the jamming.  They were very clean to start with.

From searching online, it seems the two most likely causes are solenoids sticking due to residual adhesive, and the D roller being worn, cracked, or dirty.  But neither of these seem to be the case.  I removed all the adhesive on the solenoids, and there is no other source that could put adhesive on them as far as I know.

What else could I try, either to diagnose or fix the jamming problem?  Please don’t tell me to buy a new printer; I have good reasons for trying to keep this one working.

Thanks,
Roger

[davidzuts]

Did you put a replacement pad back on the solenoid. The stickey material was what was left of a dampening pad that was glued to the ledge so when the L arm hit the ledge it did not make a loud clicking noise. If no replacement pad was put in place, then the L arm becomes magnetized and would tend to stick which could cause your issue. In other words the L arm does not immediately return to the open position. Another thing you can try is to cut 1 or 2 rings off the spring that connects the L arm to the main frame so it has less chance of sticking.

[anonanon]

Thanks for this idea.  No, I didn't put replacement pads on the solenoids (there are two), because what I'd read online was that nothing was needed.  That could be wrong, of course

Are you pretty sure that the L arm gets magnetized if there is no replacement pad?  Or just guessing?

What would you suggest using as a replacement pad?

Could you point me toward the disassembly instructions for getting to the solenoids?  I can't find them online any more; there used to be photos too.

Thanks again,

Roger

[davidzuts]

I have seen this with the carousel solenoid on the color laserjet 2500 series. As to instructions you are going to have to do it from memory as it has been over 15 years since I worked on one of those and seem to remember just removing the pickup roller was a very difficult job. As to replacement pad I would recommend a thin velco pad or very very thin furniture pad. Keep in mind what you describe is a classic sticky solenoid. When you print one sheet at a time the solenoid sticks but only for a moment and then returns in time to stop the pickup roller from turning. When you print more than one page the solenoid sticks and since there is no pause if the pickup roller being stopped the second sheet is picked up to fast and trigers the registration assembly to soon and the printer stops thinking there is a jam.

[anonanon]

Thanks again.  I will try putting a thin velcro pad in each of the solenoids.

One question:  should I do anything to demagnetize the arm that got magnetized?  Is it possible to do so?  Or is the magnetization of the arm just a brief event?  (I can't figure out why it took two years for this problem to crop up, and whether it's a problem that willget worse over time.)

Btw, the disassembly instructions were easy to find after all:

https://www.youtube.com/watch?v=-LGf0aGQhmQ

Roger

[davidzuts]

The arm will be fine. Only lasts a short period when used without having a pad.