43451HP Laserjet 4345mfp with a 13.0a.00 Jam Reading "Output Bin, Paper Stopped Jam"

We had an HP Laserjet 4345MFP giving intermittent 13.0A.00 jams.  Generally, this would happen in the middle of a job, which means there were pages everywhere inside the printer, at all stages of the print process.  One in the reverse assembly, one in the fuser, one under the cartridge, and one still being fed from one of the drawers.  As we looked continued, we could start to see a pattern...

If we ran a straight paper path test page from the diagnostics menu, it would go straight through without jamming.  But when we did the same test, enabling the duplex, then we'd get our jam.  As a matter of fact, when we did a single paper path test page (with duplex enabled), the page would spit out into the exit tray as if all was normal... but a few seconds later the machine would beep and the jam error would appear, with the message "Top Output Bin, Paper Stopped Jam."

43452Since the paper had already left the machine, I figured it had to be a problem with the very last paper path sensor that was tripped... one that only duplexed paper would hit.  That leads us to the reverse assembly, part# RM1-1022.  It has a flag the paper passes over just before leaving the machine.  True, the paper does hit the "bin full sensor" after this, but that would not have given a paper jam error.

So we replaced the reverse assembly.  We ran about 20 duplex test pages, and didn't get a jam.  We ran 20 more, and it gave us a jam on the 10th one.  So I still wasn't in the clear.

Above the reverse assembly, is the "reverse separation guide assembly", part# RM1-1019.  This was the real culprit.  As seen in the picture, a sensor flag on the assembly works in conjunction with the sensor flag on the reverse assembly (they're right on top of each other).  As you can see in the picture, the flag is just slightly worn away by years of use.  Enough so that sometimes it was not sensing the paper as it passed.