There are gaps in my printing!!! The docs are missing lines...Is it the printheads or could it be an ink problem?

For severe HP OJ 6500/6500A/7000 print quality/missing color issues, or incorrect color output, there could be an air bubble in the ink cartridge(s), an air gap between cartridge and PRINTHEAD, or a portion of the PRINTHEAD is dry (quite common), so you should first perform a CLEAN PRINTHEAD procedure from your printer control panel.
It is first suggested you print the SELF TEST or PRINT QUALITY REPORT (under TOOLS menu) to aid in identifying which color is causing the issue. Check that cartridge or cartridges to ensure they have plenty of ink inside.
NOTE: If one or more the colors were previously dry fired during printing (i.e. if you continued printing using only a few colors to one, air may have been accidently ingested into the ink lines between the cartridge(s) and PRINTHEAD. To recover from this problem, you may have to run the CLEAN PRINTHEAD procedure 2-3 times.
If a problem persists then it is suggested to review the steps outlined on the following HP 920 support pages, including printhead removal/printer cleaning and service station cleaning. It is suggested you refer to printer manufacturer instructions first as the Inkjet411 procedures are provided for general guidance purposes only. A dirty service station can cause poor image quality and/or ink cross-contamination between different colors:
http://inkjet411.retailinkjet.com/?page_id=1495
If the problem still cannot be corrected, then the PRINTHEAD may be dry and may need to be flushed (i.e. with warm water as it could have dried out, but this is a function of how much you print). Remove and thoroughly flush all ink ports for 2-3 minutes...thoroughly dry printhead prior to re-installing. Retest. For complete instructions refer to video here: http://inkjet411.com/?page_id=2412
Worst case scenario the PRINTHEAD may simply be electrically damaged or at end-of-life (while Officejet 6500/6500/7000 printer PRINTHEADS are rated for an estimated 15,000 pages, the average consumer may only see up to a 10,000 printed page throughput) and may require replacement. A severe failure of the PRINTHEAD is typically accompanied by error messages such as INCOMPATIBLE PRINTHEAD, REPLACE PRINTHEAD or INK SYSTEM FAILURE. NOTE: The PRINTHEAD will eventually fail in time. For more information on the how the PRINTHEAD works, watch the video here: http://inkjet411.retailinkjet.com/?page_id=1983
To verify Printhead electrical performance, activate the Tap 41 diagnostic test, (i.e. Pen Status: Pen OK).....for printer model instructions please visit: http://inkjet411.com/?page_id=1813
To solve other HP920 ink-series printer/printing related issues please visit http://www.inkjet411.com

try to reinstall black cartridge , if does not help try remove black ink then turn the printer off and on , when printer asking for black cartridge ,
install it , hope help you

Mohamed Hejazi
Afaqnama - libya
[email protected]

For severe print quality/missing color issues there could be an air bubble/air gaps in the printer ink lines or a portion of the PRINTHEAD is dry, so you should first perform a Clean PrintHead procedure from your printer control panel.
NOTE: If one or more the colors were previously dry fired during printing (i.e. if you continued printing using only a few colors to one, air may have been accidently ingested into the ink lines between the cartridge(s) and PRINTHEAD. To recover from this problem, you may have to run the Clean Printhead procedure 2-3 times.
If a problem persists then it is suggested to review the steps outlined on the following HP 920 support pages, including printhead removal/printer cleaning and service station cleaning. It is suggested you refer to printer manufacturer instructions first as the Inkjet411 procedures are provided for general guidance purposes only. A dirty service station can cause poor image quality and/or ink cross-contamination between different colors:
http://inkjet411.retailinkjet.com/?page_id=1495
If the problem still cannot be corrected, then the PRINTHEAD may be dry and may need to be flushed (i.e. with warm water as it could have dried out, but this is a function of how much you print). Remove and soak in hot water for 5 minutes...thoroughly dry printhead prior to re-installing. Retest.
For more information please visit:
http://inkjet411.retailinkjet.com/?page_id=856
Worst case scenario the PRINTHEAD may simply be electrically damaged or at end-of-life (typically fails between 3,000 and 5,000 printed pages) and may require replacement, usually accompanied by error messages like Incompatible Printhead or Ink Delivery/System Failure. NOTE: The PRINTHEAD will eventually fail in time. For more information on the how the PRINTHEAD works, watch the video here: http://inkjet411.retailinkjet.com/?page_id=1983
To verify Printhead performance, run the Tap 41 diagnostic test, (Pen Status: Pen OK).....for printer model instructions please visit:
http://www.Inkjet411.com

have you already replaced the ink of your black?..

Clean the printhead
If your printed output is streaked or has any incorrect or missing colors, the printhead
might need to be cleaned.
This process uses ink to attempt to unclog and clean the nozzles in the printhead.
This might take a few minutes and will use one or more sheets of paper.
To clean the printhead from the control panel
1. Load letter, A4, or legal unused plain white paper into the main input tray.
2. Press Setup.
3. Press the down arrow button to highlight Tools, and then press OK.
4. Press the down arrow button to highlight Clean Printhead, and then press OK.
The product cleans the printhead.
5. Press any button to return to the Tools menu.
To clean the printhead from the Printer Toolbox
1. Load letter, A4, or legal unused plain white paper into the main input tray.
2. In the HP Solution Center, click Settings.
Work with ink cartridges 1513. In the Print Settings area, click Printer Toolbox.
NOTE: You can also open the Printer Toolbox from the Print Properties dialog
box. In the Print Properties dialog box, click the Features tab, and then click
Printer Services.
The Printer Toolbox appears.
4. Click the Device Services tab.
5. Click Clean Printhead.
6. Follow the prompts until you are satisfied with the quality of the output, and then click
Done.
There are two stages of cleaning. Each stage lasts about two minutes, uses one sheet
of paper, and uses an increasing amount of ink. After each stage, review the quality
of the printed page. You should only initiate the next phase of cleaning if the print
quality is poor.
If print quality still seems poor after you complete both stages of cleaning, try aligning
the printer. If print quality problems persist after cleaning and aligning, contact HP
support.
To clean the printhead from the embedded Web server
1. Load letter, A4, or legal unused plain white paper into the main input tray.
2. Click the Device Settings tab, click Device Services in the left pane, select Clean
Printheads from the drop-down list in the Print Quality section, and then click Run
Diagnostic

Good luck................Pete

BETTER SOLUTION IS IF YOU TAKE MORE PHOTOS I SUGGEST YOU BUY ORGIINAL INK CARTRIDGES.THEN YOU CAN DO ONE TIME REFILLING.ITS OK.

AGAIN IF YOU TRY REFILL SAME CARTRIDGE MAY LOSS YOUR PAGE YEILD. IF U WANT USE REFILLED CARTRIDGES AGAIN BUY VIRGIN CARTRIDGE FROM REFILL STORE AND MAKE REFILL. OTHERWISE INK WILL FINISH SOON.

FOR BLACK INK U SHOULD REFILL OR BUY NEW ONE NOW. BECOS BLACK INK FINISHED ALREADY. THATS WHY YOU GETTING BLUE PRINTING....OOOOOOOOOK DEAR...

I service this unit a lot for print quality issues, and most of them come from using non-Canon brand ink. There is a solvent quality to the Canon ink that helps keep the printhead from clogging.
If you are not using it, I recommend it, especially for the big #5 ink tank.
Alignment has nothing to do with the missing print.
Use the cleaning utility in the maintenance area of the printer driver utilities to clean the printhead.
Run the nozzle check, and you should see improvement with each cleaning. Do not run the cleaning more than maybe 5 times, and never use the deep cleaning, you are just wasting a lot of ink.
If you don't see any improvement, stop cleaning and take the unit in for service - we have sonic washers and other effective methods for cleaning and flushing the printheads without damage.
You can replace the printhead yourself, but it will cost less to have it cleaned.

Here is a full detailed explanation on how you can avoid Epson printer skipping lines

https://www.errorsdoc.com/epson/how-to-fix-epson-printer-printing-with-lines-missing-or-printer-skipping-lines-issues/

The head of your printer cartrige (black) are not detected by the printer because it was damage and need to be replace. So that no more black ink could print anyway.

Possible printhead issue.
Please reseat the black cartridge. Let the printer charge like it normally does.
Print a nozzle check pattern. If you see gaps, missing lines or missing colors on the pattern, clean the printhead using the driver. 3 consecutive cleaning cycle is recommended. Compare the nozzle pattern over the last printout. If you see any improvement, you can clean the head numerous times until you get a perfect nozzle check pattern.