HP Office Jet Pro 6978 print problem

[Winj]

My printer seemed fine until yesterday when it stopped printing.  I have replaced the color and black cartridges and cleaned the print heads (via internal printer program).  It still won't print anything black on the test page.  It prints color, but not black.  What else can I do?

[Bob_Headrick]

The troubleshooting steps in the document here may help resolve black not printing on your Officejet Pro 6978.  

If the standard troubleshooting did not resolve black not printing I would suggest removing the black cartridge.  Turn it over and examine the area around the ink port.  There are four orange plastic spots, left over from the protective cap.  Make sure these are flush with the cartridge body, if not carefully trim them flush.  If the plastic nubs protrude they can prevent the cartridge from seating properly.  Before replacing the cartridge in the printer dribble a few (maybe four) drops of hot water into the ink port in the printer and two drops into the ink port on the cartridge then snap the cartridge back in position.  

It may also help to manually clean the printhead as described in the post here.

I have also seen cases where leaving the printer overnight after the cleaning cycles allows black to recover.

If none of the above restores black printing your printer will likely require repair or replacement.

[OldTV]

I have the same problem but only the cyan color doesn't print.

[Bob_Headrick]

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@OldTV wrote:

I have the same problem but only the cyan color doesn't print.

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Assuming you have an Officejet Pro 6978 I would suggest you go through the same troubleshooting steps as listed in my post above, except substitute "cyan" for "black" above.  In particular, be sure to verify the plastic nibs are trimmed, the vents are cleared and the latch latches properly.