MrCreosote

asked Oct 13, 2011 at 11:58am
Hp HP LaserJet 4

HP 7200 series D7260 dog ear paper jams

Does this to RHS LE (leading edge) of sheet.

Suspects:

1) Articulated black finger at rear of paper tray,
2) Paper tray slop and misalignment,
3) Rear hatch slop and misalignment.

Damages 80\% of all types of paper.

80\% of the dog ears do not jam but are ruined prints.

The 4 rear powered rubber rollers are nice and soft and tacky.

Any thoughts?

Thanks in advance,
Tom
Dog ears are caused by the paper encountering some sort of obstruction. Usually it's a scrap of paper or a piece of label that came off. To fix it, I run a piece of stiff plastic into the paper path at the place where the defect is occurring. In the absence of stiff plastic, then you could use a stiff piece of cardboard like a file folder.
by moe on Oct 13, 2011 at 12:04pm Add comment
Thanks, I'll try that tomorrow at the office.

One thing I did try yesterday was to see if I could manually push a sheet of paper into the paper path because from the sound of the jam, it sounds like the damage is done as soon as the paper begins to move.

I took two pieces of letter paper and taped them into a "long legal" length. Then I put some longitudinal accordion folds in it so it would not buckle when I pushed it inward.

I found that the page bucks up against the back of the tray with no hope of turning upward into the paper path. That suggests my belief that the first part of paper movement is to form a momentary leading edge buckle - probably to separate sheets stuck together.

What was very interesting was that the leading edge of the paper was "dented" by something relatively sharp when I tried to push it rearward.

The feed force appears to be a pair of rubber rollers that contact the paper top somewhat aft and rightward of the center.

The only mechanism that moves and contacts the LE of the paper at the beginning of its feed is the little near vertical black finger into which the LE bucks up against. The contact surface of the finger is dimpled so the LE cannot slip vertically.

Again the theme that a momentary buckle is produced at the start of paper movement.
__________________-

It could be possible that something may have lodged or broken off in the paper path which is past the 4 rear feed rollers and before the printing area. This part of the path cannot be viewed due to the way the mechanism is built.

But for sure, the dog ear is present before the LE reaches the print area.

There is a small horizatal "black finger" paper sensor which rests in a nest in the paper path of the back access panel. I have speculated that the back panel is lose which would let this finger protrude.

It seems like there is a reduction of paper damage if this back panel is manually pushed into the printer as far as it will go.

While pressing the panel inward, there are substantial forces that you can feel pushing on the inside of the panel. This is quite unexpected because the only thing that really contacts the back panel are its attachment points, the 4 aft rollers, and the paper itself.

So what is "bumping" it from inside the printer?
_________________

If I get really curious, I have an articulating bore scope (medical endoscope) that I can snake into the printer and observe paper motion at a number of stations. This could be very entertaining!

Thanks for the tip too!
Regards,
Tom

by MrCreosote on Oct 13, 2011 at 5:07pm Add comment
I have a weak theory which could explain the black finger problem.

IT could be that during a bad paper jam, paper was rammed behind the black finger, bending it forward.

In its bent state, it can no longer retract properly and the paper hits it all the time.

Of course, I would need to see a good one to know if I'm right. When viewed from the side (can be easily seen with the rear panel removed) it is definitely not a straight finger but is bent at about mid-span.

An interesting problem and I'm really surprised no one has figured this one out since this is a rather common malfunction.
by MrCreosote on Jan 15, 2012 at 10:20am Add comment
The paper sensor fingers are bent. This allows the paper to slide over them. If they were straight, the paper would hit them and stop since it's not rigid enough to push it down. The other end of the arm interrupts an optical sensor which signals the electronics that the paper has reached or not reached that point. Like I said, I've dealt with this issue thousands of times and 99.9\% of the time, pushing something thin, flexible and rigid along the paper path pops out the offending object. This thread on similar jams lists hundreds of strange objects like cat claws that have been ejected using my methods. http://www.fixyourownprinter.com/forums/printer/29793
by moe on Jan 16, 2012 at 10:47am Add comment
Moe,

Wow, what a long interesting thread. I scanned it (rather than reading it carefully) and still found a lot of bizarre "little things" that screwed up printers.

The D7260 is such that if you remove the paper you can see all the principles at the back of the paper tray. With a good LED light there isn't much you can miss. Even used dental mirrors to look from the back access panel.

I'm about due for another scrutiny - I've not given up yet. Problems like these are puzzles for me. Other people like Suduku.

My biggest problem at this point is why there are 3 fixed vertical but backward leaning serrated fingers on the back of the paper tray and why there is a single black vertical serrated finger that the leading edge of the paper bucks into the instant its starts to feed.

Non-photo printers have nice smooth paper paths that make total sense.

Like the 3 fixed fingers... WHY aren't they smooth? Instead they have "teeth" one the side the paper contacts. Teeth about the size and pitch of a carpenter's saw. WHY?????? The paper leading edge will get stuck in these!

I just don't get it. If I understood what is supposed to happen, I'd have a better diagnostic chance.

I need a video borescope where I can record a movie when the paper feeds (!) HaHa

Tom

PS. I took photos of the paper jam in its infancy by pulling the power supply the instant the paper moved. Photos are located here: http://h30434.www3.hp.com

I also need to take a photo of the ABF (articulating black finger) which can be seen from the side where it could be compared to a working D7260 to see if it is out of place or bent. May take a while since my home computer mobo/cpu has failed and I haven't repaired or replaced yet and that was where I did all my photo work.
by MrCreosote on Jan 20, 2012 at 10:24pm Add comment
SOLVED:

CAUSE: Malfunction of Service Station Carriage - it would not nest properly when print head undocks due to ink buildup and possibly the squeegee rubber coming loose and laying in the carriage. (Print head was never sealed properly! The rubber seal left 1/2 the print head exposed. No wonder it "clogged" overnight.)

REASON FOR JAM: The articulating black finger is driven by the service station carriage. If the carriage cannot nest properly when the head undocks, the finger does not articulate out of the way.

REPAIR: Just clean everything out with hot water. However, printer must be disassembled completely down to the bare sheet metal chassis!!! It is not that bad a job if you know how to do it - which I do now. (I'm probably the only person in the world that has done this repair.)
by MrCreosote on Jan 21, 2012 at 8:53pm Add comment