m607n detects incorrect paper size when tray 2 is full, but properly detects when partially full

[Flier71N]

We have 22 Laserjet m607n's in our enterprise.  Three units have the exact same issue which I have been unable to resolve.

Issue:
When tray 2 is more approximately half-full, it incorrectly detects the size as A5. I can repeatedly open and close tray 2, and it will detect as "Plain, A5" about 19 out of 20 open/close cycles.  Rarely, it will detect as "Plain, Other" or as "Letter."  We use plain 8.5 x 11" 20-lb paper exclusively.

Upon inserting the tray, the printer will lift and display what it detects.  When it incorrectly detects as A5, selecting "modify" and choosing "letter" results in the printer displaying the notice "The size is currently unavailable. The guide positions do not match the size."  The size selectors in the tray are correctly set and locked into position. Not once have the size selectors been improperly set.

Removing paper such that the tray is 50% full, and the detection rate is flipped; it will properly detect as "Plain, letter" most of the time.  At half-capacity, when it does detect as A5 or other, simply opening/closing the tray will resolve it, but not when the tray is full.

Troubleshooting Steps Taken:

• Confirmed the paper size guide is properly set at 8/5" x 11."  I never discovered it incorrectly set.
• Changed the size guide in tray 2 to something other than letter but this has no effect on the proper detection rate.
• Confirmed the tray is not over-filled. We can take an empty tray, place a new ream of 500pgs, and it will mis-detect nearly every time.
• Thoroughly dusted using an air compressor, not canned air.
• Installed new HP maintenance kit.
• On one printer, I replaced the tray 2 pickup rollers with new twice (thus three sets of rollers).
  • Confirmed installation of the the pickup rollers did not somehow clip the paper height lever.
• Swapped tray 2 with one from another working m607, eliminating the tray as the cause.
• Checked the size detection switches in the tray 2 bay are not obscured by any debris.
• Tested sensors via the the Manual Sensor Test.  I depressed and released the four detection switches 20 times each, the test detected the close/open state each time without fail.
• Cleaned what I believe is the tray 2 media out sensor with a cotton swab.
• Upgraded firmware.
• Factory reset firmware and tested from factory settings.

Each of the three printers experiencing the issue have between 200k to 250k print cycles.  I do not understand how the capacity of the paper tray affects size detection.

Has anyone else experienced and resolve this issue?

[Repairatrooper]

When you did the factory restore, did you format the drive and reinstall current firmware? I have not run into this error with the 607 series engine and we have a couple hundred under contract with customers. I would suggest that if formatting the drive does not resolve the issue you may want to open a support case with HP tech support. This forum is just a user to user forum.

If I was faced with this issue, I would do the following. Replace the size sensor board, replace the tray 2 pickup assembly  and finally replace the DC controller. One at a time in that order, not all at once. 

Thank you for posting a quality question, it makes it much easier 

[Flier71N]

Thank you and I appreciate the quick response.

I factory reset twice; first using "Reset Factory Settings" in the web console and second by selecting the "Reset Firmware" checkbox when performing the firmware upgrade.  I cannot find an option to format; none of the units have an HDD.

Unfortunately, the units are out of warranty and HP will not help.  I posted here hoping someone might have experienced and resolved the issue.

I don't see a size sensor board listed in the service manual, just the size sensor, which the manual sensor test deems working.  I'm going to replace the DC controller first, it's fairly cheap and easily accessible.  Getting to the tray 2 pickup assembly requires significant disassembly.

Thank you for your recommendations.