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Open the lid of the unit and take out the printheads (then unplug the printer):
Lift the handles on all the printheads and take them out.
Wipe any ink from the electrical contacts on the printhead with a q-tip dampened in hot water. Then, use a soft lint-free cloth to dry it off (Shown as #1 in the picture below, don't touch the nozzle, item #2):
Do this for the ink cartridges copper contacts as well:
After the electrical contacts on the printhead and cartridges are clean and dried for a short time, set them aside (make sure the nozzle on the bottom doesn't come in contact with anything).
Use a fresh soft lint-free cloth to clean the electrical contacts see inside the printer where the printheads sit.
Look in the center of the product for the four ink tubes that connect to the printhead, and then examine the ink tubes. The ink tubes should be bundled neatly, and they should not appear kinked or bent.
Shake the printheads back and forth about 5 times, then reinsert them along with the ink cartridges. Close the printer, and plug it back in and turn it on.
Now print a test page, on the control panel press the setup button > Tools > Select Clean Printhead
Look at the test pattern, if some of the blocks show white lines, clean the printhead 2-3 more times this way until they are gone. If there are white lines through all the blocks, including the gray blocks at the bottom of the test pattern,
Skip to this step:
Go back to setup > Tools and Select Calibrate Linefeed and press ok
source: hp.comIf you cannot print any test pages at all, then the printer will instead need to be serviced by HP. Please call 1-800-474-6836 to get a quote on the repairs (if it is within warranty they will be covered).
If you can print a test page but cleaning and calibrating does not take the white lines out, then one of the printheads need to be replaced, see below:
Black block has lines -replace Black/Yellow printhead.
Red block has lines - replace Black/Yellow printhead.
Green block has lines - replace Black/Yellow printhead.
Cyan block has lines - replace Magenta/Cyan printhead.
Magenta block has lines - replace Magenta/Cyan printhead.
The ink goes through these and sprays onto the paper, and if they are partially clogged or worn out, you will get horizontal lines and other printing defects. This is can happen and doesn't indicate anything mechanically wrong with the printer. Click HERE to determine the warranty date of the printheads, then call 1-800-474-6836 to get replacements.