HP DeskJet 6940
I set my printer to “Black and White” but it prints in red. I’ve tried several things, but nothing seems to work. AND the toner cartridges are new.

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How to Identify and Fix Common printer Problems ?

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If your HP printer not printing black ink correctly, here`s what you should do. Using non-genuine ink cartridges. Printheads that have become clogged. Ink cartridges that are defective or empty.
Check you have the latest drivers installed for your printer, try uninstalling and reinstalling your printer drivers or try changing the driver settings (adjusting the paper settings has been known to solve the problem). Fully Reconfigure the Printer – If all else fails, you can try entirely reconfiguring your printer.
Check the ink levels

Sometimes, the printer may not print black ink because it is low or empty. You can check the ink levels on the printer`s display, or by using the software that came with your printer. If the ink level is low, replace the cartridge or refill it according to the manufacturer`s instructions.

If your PC or the LCD screen on your printer is telling you that your ink cartridges are full but no ink is passing through to the paper, then it`s most likely that you are dealing with a clogged printhead. Blurry documents and images that appear faded are also signs that it`s time to remove the excess ink.
Even if your cartridge is full and ready for action, it may have become slightly dislodged and no longer in full electrical contact with the printer. The easiest way to rectify this potential problem is to simply remove and reinstall the cartridges.
Just above the circuit board on most printer cartridges, you`ll find a small button. You`ve seen these tiny buttons before on cell phones, phone chargers, etc. This is your reset button, and the only way to get in there is either with a paper clip or the tip of a pen (which will leave a tiny ink smudge on the button).
You can continue to print with one or more empty cartridges, but HP recommends replacing them as soon as possible to avoid printhead damage.
If you cannot cancel printing from the computer, cancel using the printer`s control panel. Select System Preferences from the menu > Printers & Scanners (or Print & Scan, Print & Fax), and then select the printer. Click Options & Supplies > Options (or Driver). Select On as the Permit temporary black printing setting.
There are a number of reasons why ink is not flowing through the cartridge, despite there being plenty of ink in the cartridge. The most common cause for this is infrequent usage. If your printer is not used on a regular basis, at least once a week, the cartridge can dry up and then become clogged as a result.
Ink cartridges can dry out over time. If they are sitting in your machine for an extended period, they will eventually dry up and become unusable. The simplest way to combat this problem is by printing more frequently or running regular cleans and ink tests to ensure the nozzles remain clean.
When your run out of black ink you may still be able to print using color ink. InkJet printers will sometimes allow you to make a print in blue, magenta, or whatever colors are available.
How to Switch to the “Color Only” Setting. Not all printer models will have this option in their settings menu, but it is worth a look. If you are out of black ink and only want to print with the color cartridges, see if your printer has a “color only” setting.
How can I override my HP ink cartridge? Remove and reinstall the indicated cartridge slots 2-3 times until it firmly sits in place to override the HP ink cartridge error. After doing this, turn off the printer and remove all the cartridges.
In Windows, go to Printer Properties > Maintenance > Clean Heads > OK and follow on-screen prompts.
The warranty period for the printheads is 1000 cc of ink through the printhead (previously 700 cc), or the expiration date printed on the printhead, whichever comes first. However, printheads may last much longer than 1000 cc of ink. On average, printheads should last through 2-3 ink cartridges.
Whether you use an HP printer or any other, you can make it possible to print in black while your printer screen is showing the color cartridge empty notification. All you need to do is reset your printer first and then, make certain print settings i.e open the option of “Print in Grayscale”.
The shelf life for an original printer cartridge is 24 months and the shelf life for a compatible cartridge is 36 months. Over time, ink dries out and settles inside the cartridge, which can cause your printer to clog.
Turn the product on while you press and hold the Resume button for 10-20 seconds. The Attention light turns on. Release the Resume button. The Attention and Ready lights cycle while the product restores factory defaults.
Turn the printer off. Disconnect the power cable from the printer for 30 seconds and then reconnect. Turn the printer on while you press and hold the Resume button for 10-20 seconds.
HP 680 is not a compatible cartridge for your printer.
When color ink is expended and black ink still remains, you can continue printing for a short time using only black ink. However, you should replace the expended ink cartridge(s) as soon as possible.
Toner can only print in black (or very dark colors), so if you try to print something white on black paper, the printer will not be able to produce an accurate image. Printers use ink to create images on paper and this ink is typically transparent.
To underprint, or print white on black paper, you simply swap the traditional position of the white toner cartridge in the printer with the cyan cartridge by moving it to the last slot. There`s no flushing the lines or any of that – you literally just pick up the first and last cartridges and move their positions.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

wont print black when all commands tell it to do so
ANSWER : Awesome..You have clearly explained …Its very useful for me to know about new things..Keep on blogging..

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HP DeskJet 6940

changing from printing in photo black to black ink
ANSWER : You can change the black ink cartridge and choose either Matte Black or Photo Black.You will need to use the Black Ink Conversion Kit that came with your printer. The kit includes three conversion cartridges (yellow, magenta, and cyan), which are used to reduce the amount of ink consumed in the conversion. dissertation writing service

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HP DeskJet 6940

when printing front and back, the front will print well but the back will fade
ANSWER : It happens because second side voltage is much higher and the board breaks. Are you getting this issue in auto duplex only, or same error you are getting when you print second side manually?

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HP DeskJet 6940

PRINTER FAILS TO PRINT BLACK TEXTS/IMAGES
ANSWER : https://www.youtube.com/watch?v=f57jOGj-G5s

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HP DeskJet 6940

Canon i560 Will not print black
ANSWER : Dang, it worked for me then wentback to normal (not working) after the test page. Oh well not bad for a 10 year old bubble jet.

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HP DeskJet 6940

C1660w black printing light
ANSWER : Have someone fixed this? I have the same problem. Please help.

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HP DeskJet 6940

HP Deskjet 640c wont print??
ANSWER : yes

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HP DeskJet 6940

black cartridge not printing
ANSWER : https://www.youtube.com/watch?v=thrZtvAhKm0

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HP DeskJet 6940