Canon PIXMA MX870 Service Manual page 36

(3) Printer unit removal, and ink absorber replacement
1) Separate the PictBridge chassis from the main PCB chassis. (1 screw)
2) Separate the main PCB chassis from the bottom case. (1 screw)
3) Separate the PCI DC and GND harnesses from the printer unit. (1 screw)
<The GND harness fits to the bottom case rib.>
See "4-5. Special Notes on Servicing, (7) Power supply unit and modular board replacement."
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