HP Deskjet 6540 Color Inkjet Printer - Manual (Page 148)

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.
16.1.2 Automatic two-sided printing problems
Paper jam occurs inside the Automatic Two-Sided Printing Accessory
Paper jam
Follow these steps to remove a paper jam from the duplexer.
1. Turn off the printer.
2. Press the buttons on the left and right sides of the duplexer, and then remove
it from the printer.
3. Remove any paper inside the printer.
4. Open the duplexer.
HP Deskjet 6500 series printers User's Guide
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