Canon PIXMA MX860 series Getting Started page 7

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Open the Paper Output Tray (A), then lift the Scanning Unit (Cover) (8) until it locks into place.
Close the Document Cover (C) and lift it with the Scanning Unit (Cover).
The Scanning Unit Support (D) is fixed automatically.
The Print Head Holder (E) comes out. (This is where you install the Print Head.)
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• Handle the Print Head carefully. Do not drop or
apply excessive pressure to it.
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• The Print Head Holder makes a noise as it moves. This is normal operation.
• If the Print Head Holder does not move, make sure that the machine is turned on.