HP M400 series color printer duplex jam

[dgangstee]

I wanted to respond to a post (answer) that David from HP posted back in 2019 about paper jamming in the m451dn duplexer. I'm not picking on David but I have been repairing LaserJets since the very first model and I want to set the record straight.

David responded to a member that had an issue with paper jamming in the duplexer when printing double sided. David spoke about only the duplexer models having a (green pull down) tray above tray #2 and that might be an issue.

Having repaired several of the M400 color series I know that all of this series have that tray above tray #2 and it has no relation to the duplexer. Even non-duplexer printers have this tray. Its sole purpose is to transport paper from the #1 (manual feed) tray to the rear intake paper guides so it gets fed to the transfer belt area. Even if printing duplex the paper passes through this tray once upon feeding and the duplex printing is done the same from that point as would paper being fed from other paper trays. While it is possible to have a paper jam in this tray it is not related to the duplexer as it is only a transport from the manual #1 tray.

Now about the jam in the duplexer. I have found that many times this is related to the lower paper guide that paper from tray #3 if installed passes through. This paper guide can come loose as it is held in place by a single catch and if it comes loose it can move into a position where it sticks slightly up into the duplexers lower exit area where paper is returned to the transfer belt area.

When duplex printing the paper partially exits from the fuser after printing the first side and is pulled back into the printer and a paper guide above the fuser flips so that the paper is redirected into the top of the rear mounted duplexer and it travels down the duplexer and does a u-turn and travels back through the transfer area but is now turned over in this process so that printing is now on the back side.

It is at this u-turn area where the paper path comes close to the lower intake paper guide (no relation to each other but next to each other) that I mentioned above and this is a frequent place for the paper to jam. You can tell because the paper will be scrunched up in this area and if you look close at the leading edge of the paper you may spot an area that  shows an impact to the paper where it snagged on the lower paper guide if it is out of position and protruding even slightly up into the duplexer exit path.

This lower paper guide can be accessed from the underside of the rear end of the printer by removing a metal plate (the one second from the rear of the printer) and re-attaching the plastic paper guide to the metal plate. Its a bit tricky as the paper guide has some short wires connecting to a sensor making it difficult to re-attach the plate to it and to get the assembly into position to re-attach it to the printer. Also there is a plastic arm attached to another paper guide that must be re-attached to a stub (it just slips on) on the lower paper guide as you re-attach it to the printer. This will be a lot of fun indeed.

Sorry for being so long winded but I wanted to thoroughly explain this issue so that others would be helped in troubleshooting their M400 series color printers. Finally be sure to keep the paper paths free of any debris to reduce the probability of other jams.