HP Photosmart 6520 not printing black

[Kintsugi]

My HP 6520 printer had been printing light gray for the last couple of days, and now since two days it has not been printing black at all. Color works just fine. I thought that the cartridges were the issue, and I tried replacing the cartridge to no avail. I have only ever used HP cartridges. I tried the clean printhead function, and print diagnostics, the text prints out dark grey, but the black box remains blank. I researched the problem in these forums and tried various suggestions, such as disconnecting and reconnecting the printer, ensuring that the vents on the cartridge are clear. I am at a dead end. Grateful for your inputs.

[Rainbow23]

Hi @Kintsugi,

Welcome to the HP Support Community. 

This could be a hardware issue with the unit and may need repair. 

I have sent you a private message with the required information to talk to HP Support. 

In order to access your private messages, click the Private message icon on the upper right corner of your HP Community profile Next, to your profile Name, you should see a little blue envelope, please click on it or simply click on this link