HP Deskjet 6940

Hi
It sounds like a good chance the black has blocked it does not take much just things like leaving the cartridge out for a bit or it can also take a bit to get a new cartridge working.
I would recommend you try to do a head clean it uses a lot of ink doing this but sometimes there is no choice.
In settings you should be able to do only black option.
Regards Craig

if you are not buying NEW OEM cartridges they will never work properly. and once installed if they are oem they will not work the second try either .

I have an HP DeskJet 1220C that has been working fine for two years now. All of a sudden it can only print in pink and black. It is driving me crazy. I have tried the following without any success:

1. Replaced the cartridges twice
2. Aligned and cleaned the cartridge from the
computer
3. Soaked the cartridge head in hot water,
and made sure that all three colors will bleed
out of the head
4. Cleaned the cartridge contacts with an eraser
5. Cleaned the cartridge contacts on the printer
with a brush

Is there a cure, or is it time for a new printer?

This is typical cartridge problem.Which cartridge changed?This printer can print with the only one cartridge inside it, whatever which.Try this: Open cover put out color cartridge then close cover.If blinking stops replace color cartridge.If blinking continues put out black cartridge and put in color.If blinking stops replace black cartridge, if not stop replace both cartridges.
If this not help your printer has problem in carriage unit and need repair.

Please remove the cartridges from the printer. Take a dry lint free paper towel and gently wipe the contacts on the back of the cartridge (not the bottom from where ink is present). Wipe the contacts inside the printer (on cartridge carrier). Please snap the cartridges back into the cartridge carrier and please try to print a printer self test.

Your printer doesnt support HP348 cartridge.
HP 99 Photo is the cartridge meant for 6940 which wud go in the slot for black cartridge. and you can print approx 130 photos .

My HP Deskjet 6940 is not printing. The color (left) low ink light is dark and the black (right) low ink light is flashing. I replaced the black ink cartridge with a new one but the low ink light continues to flash. No tears/rips in the circuit strip and all the copper leads appear to be connected

Change the color cartridge and see what happens.

The Deskjet 6940 will only show ink level for original HP cartrdgies. Refilled or reman cartridges will show as empty or unknown in the toolbox. This is not an issue with the driver, the cartrdige itself has information that it has been previously used and this is not resettable. You can continue to print with a cartrdige that has unknown ink levels, you will just not get low ink warnings.

Regards,
Bob Headrick, Micosoft MVP Printing/Imaging

Pop out the cartridge and look inside the printer where the black cartridge goes. There may be punctures in the ribbon cable from the metal wire that rests against the catridge. I have lost 2 6940's to this problem.