Hi
Welcome to HP Forums, this is a great place to get support, find answers and tips.
Thank you for posting your query. I'll be more than glad to help you.
I understand that you are facing issues with your HP Photosmart 6520 e-All-in-One Printer wherein it does not print in black.
This issue could occur if the cartridges are not vented properly or the printhead may be defective, damaged or expired.
Let's go through a few steps that may help to fix this issue.
And here are a few steps in the link: Black Ink Not Printing
Note: This model of the printer does not have a removable printhead. Hence, the complete unit needs to be replaced.
You may also contact HP phone support from this link: www.hp.com/contacthp
You may select the country and type the product# of the unit and then follow the on-screen instructions to contact HP phone support.
You have a good day ahead.