HP Deskjet 6840 Color Inkjet Printer - Manual (Page 146)

Note: Do not press the buttons on either side of the duplexer when installing
it in the printer. Use the buttons only when removing the duplexer from
the printer.
12.1.2 Automatic two-sided printing problems
Option for automatic two-sided printing cannot be selected
Verify the following:
• The duplexer is attached to the printer.
• A supported paper size is selected in the
Page Setup dialog box.
• A supported paper type is selected in the Paper Type/Quality panel of the
Print dialog box.
For a list of support paper types and sizes, see the duplexer specifications .
Only one side of the page prints when the two-sided printing option is
enabled
Verify the following:
• The correct print options are set in both the printer software and the application
you are using.
• The photo paper is not curled, if you are printing on two-sided photo paper.
Photo paper should be flat before printing. See storing and handling photo
paper for more information.
• The paper size selected in the Page Setup dialog box is supported by the
duplexer.
• The paper type selected in the Paper Type/Quality panel is supported by the
duplexer.
See the documentation that came with the duplexer for a list of supported paper
types and sizes.
HP Deskjet 6800 series printer User's Guide
146