Canon DR-5010C - Manual (Page 74)

72 Regular Maintenance
2.
Place the shaft of the pickup roller on the hooks, and then press it into place.
3.
Make sure that the shaft of the pickup roller is correctly inserted.
4.
Close the Upper unit slowly. Be sure that the Upper unit is completely closed
by pushing on both edges with both hands until you hear a click.
IMPORTANT
Do not force the Upper unit to close. Doing so may damage the scanner.