How to Disassemble an HP 3310 Printer for Repair

Unplug the printer. Do not plug it back in until it is fully reassembled.
Remove the rear access door. You'll find this taking up the bottom half of the back of the printer. Slide the small catch left to detach.
Remove the duplexer. This is the long tube-like structure right behind the door. You can just slide it out.
Open the cartridge access door by sliding your hand under the front panel and lifting up.
Remove the ink cartridges (five little colored boxes and one black box, all in a row) by pressing down on each individually. This will pop them up and out.
Remove the toner bar. This is a long cylinder behind the cartridges. It will come out with a little gentle wiggling.
Reassemble the printer after repair. Do not plug it back in until you are finished.