HP Color Laserjet 3700dn Jam type problem

[Gellenb]

I have a CLJ3700dn that is giving me a headache, and embarrassment. I've been servicing HP's since the LJ II, and this is the first HP that I'm hitting a brick wall with, and I don't have any other of these to look at. So anyone has run into this problem your thoughts are appreciated.

Single sided printing is perfect, no issues at all.
So this problem only exists in duplexing as discussed below.

Duplexing is where the issue is. To duplicate the problem:
Printer must be cold, or not used for at least 10-20 minutes.
First print job only,
-- if just one sheet of paper, both sides, no problems - USUALLY.
-- more than one page, first job paper "jam" error 13.20.00 Jam Inside Front Door
Remove both sheets of paper, close it up, restarts print job no jams. Any additional print jobs, even large jobs 50 pages + sent are fine, no jams, unless it sits 10 minutes or so.

What I see:
Paper feed all seems to be fine. It appears to be a timing issue. My guess is something is moving too fast or most likely, too slow. There is no place where paper has actually "jammed".
As show in the picture attached, when you remove the toners, you can see the two pages. One that appears to be the first page to print that has gone through the duplexer and now is in the fuser and probably 60-70% through.
Second page has now come out of the tray (or manual feed) and is being processed. There is usually 1/4" between the two pages as seen in the picture, and the picture shows where it stops.

Printer sounds good, no noticeable slow clicks, sounds, grinds anything out of the ordinary.
When stopping the printer when running a good print job the distance between the pages seems to be about the same.
In this picture, I have pushed the paper down a a bit. Otherwise, the camera makes it look like one page. Normally the two pages align with each other, with a ~1/4" of space between them.

3700.jpg

[GIUBOSS]

Have you checked any flag sensors and solenoids? The fusing unit could also affect the duplex, how many prints did it make?

[Gellenb]

Flag sensors all move freely, clean optics too. No sticking or "gummy" solenoids. Fuser was recently replaced because of quality issues, has 1700 pages on it, and problem has existed for over a year. (It's one in my office, not a customers - luckily. . . I fix my stuff last) Fuser is from HP - not a re-manufactured/rebuild/third party.

Do you think the separation between the two pages is close to normal, or should there be more space between them?

[GIUBOSS]

Flag sensors all move freely, clean optics too. No sticking or "gummy" solenoids. Fuser was recently replaced because of quality issues, has 1700 pages on it, and problem has existed for over a year. (It's one in my office, not a customers - luckily. . . I fix my stuff last) Fuser is from HP - not a re-manufactured/rebuild/third party.

Do you think the separation between the two pages is close to normal, or should there be more space between them?

I think the distance is normal, did you also do a single duplex print?

[Lance15]

You might find something that could be a clue in this document.

3500, 3550, 3700 - 13.20.00 or 13.05.00 Error Message with Paper Jam.pdf

[Gellenb]

A single page double sided document prints without issue. Only when there is more than one sheet of paper - and double sided going through the duplex.