HP Q3948-67903
The Q3948-67903 is the Automatic Document Feeder paper handling mechanism for the Color Laserjet 2820 / 2830 and 2840.
List of printers that definitely use this part CLJ2820/2830/2840
Other printers are very likely to use this assembly; HP information does not confirm this at present.
This part includes those found in the 5851-3580 Load Arm Bogie (which in turn contains the C8187-67533 Bogie itself). If the only issue is feed problems the ADF Bogie Kit Q3948-67904 is the first repair to try. Only if that fails is this whole mechanism likely to be needed.
The Q3948-67903 is intended as an engineering part and does not come with fitting instructions. The 5851-3580 Load Arm Bogie and the Q3948-67904 Bogie Replacement Kit do contain instructions.
This part will be needed if a problem with feeding does not seem to be purely related to initial paper feed - if paper scans skewed or does not reurn to the output tray correctly. If changing the feed-roller bogie Q3948-67904 (or the Pick Load arm and bogie 5851-3580 as appropriate) doesn't work then a whole assembly is needed.