I see that you're experiencing print quality issues with your HP Officejet 6500 Printer. I would be happy to help you and please remember to return to this thread and mark 'Accept as Solution', if I have successfully helped you resolve the issue. If you wish to say 'thanks' for my effort to help, click the 'thumbs up' to give me a Kudos.
I understand the frustration that you're experiencing. It sounds like there is an issue with the ink delivery system. iF you have replaced the ink cartridge and the printhead already.
If you have already performed the steps within this guide, there is a hardware issue with the device.
HP Officejet 6500 Printers - Color or Black Ink Not Printing, or the Printed Page is Blank or Prints with Little Ink