hp m479 duplex jams

[tmw]

This shows varying jams 13.09.08, 13.13.08, 13.09.14. Basically will print first side, pulled back through output and just stops when entering duplex turn around area. I couldn't find any obstruction stopping it as I could tell. Sensor flags were toggling as they should. I could see the entire paper edge in the slot where it goes into the duplexer, doesn't seem to be a blockage. I cleaned all the feed & transport rollers. There was no room in his space, and he didn't want me to take it to the shop to really get into disassembly. So, I'm not sure of a good way to determine if it's a sensor problem, or if it's not being pulled back into the machine fast enough. Just watching by eye seems to be working as normal, but who knows. Also had the fuser out and it doesn't appear abnormal. I appreciate hearing from anyone who may have run across the same thing. Thank you.

[Mroq]

Check duplex solenoids/clutches if work correct when flipping the page.

[tmw]

I was able to bring this to the shop and it is defying logical diagnosis. The current consistent code is 13.13.08. It always just stops in the duplex turn around feed unit. Since this contains a sensor and clutch it seemed like a good candidate to be faulty. Replaced it and no change. The only other parts I had available to try was the duplex motor and the connector board it plugs in to. If it's the fuser, why doesn't it get caught in the fuser ? The duplex reverse drive unit is only a gear cluster. No clutches, sensors, switches, or broken teeth. Maybe the D.C. controller ? I don't think it would work out best if I start ordering a mess of parts to just to try. I need a better way of narrowing it down. The manuals don't even fully list the error codes and explain them how they used to. There aren't any sensor or service tests on this machine. The timing where it shoots the page through the output and pulls it back seems like it's normal, but who can tell for sure ? I would like to get this fixed for the guy. But maybe it's not worth it for this machine ? Please if anyone knows something I don't I would be grateful to hear it. Thank you