Black line when printing -

[KarenM6]

HP LaserJet pro 7740

I just printed a 42 page double sided document.  Starting on page 4 and every even page thereafter, there is a black line along the left margin.   This has happenen consistently since I got the printer.

[Max3Aj]

@KarenM6, Welcome to HP Support Community. 

Thank you for posting your query, I will be glad to help you. 
The issue you’re facing with your HP OfficeJet Pro 7740 (assuming you meant OfficeJet rather than LaserJet) sounds like a recurring duplex printing defect. The black line appearing only on the even pages suggests a problem with the duplex unit, rollers, or printhead alignment.

Troubleshooting Steps

Clean the Printer's Duplexer and Rollers

1. Turn off the printer and unplug it.
2. Remove the duplexer (duplex printing accessory) from the back of the printer.
3. Check for any ink buildup or debris on the rollers.
4. Use a lint-free cloth lightly dampened with distilled water or isopropyl alcohol (90% or higher) to clean the rollers.
5. Let it dry and reattach the duplexer.

Check for Printhead Alignment Issues

1. On the printer's control panel, navigate to:
2. Setup > Printer Maintenance > Align Printhead
3. Print an alignment page and follow the instructions.

Clean the Printhead

1. Open HP Smart App (if installed) or navigate on the printer to:
2. Setup > Printer Maintenance > Clean Printhead
3. Run a cleaning cycle and test print.

Check for Toner or Ink Smearing

1. Print a single-sided document to see if the issue appears.
2. If the black line only appears in duplex mode, the issue is likely with the paper path or rollers.

Update Firmware & Drivers

1. Go to HP support site and check for firmware updates.
2. Update drivers if using Windows:
3. Open Device Manager > Printers > HP OfficeJet Pro 7740 > Right-click > Update driver.

Try Different Paper & Orientation

1. Ensure you're using HP-recommended paper.
2. Try changing the orientation (portrait vs. landscape) and see if the line moves.

I hope this helps. 

Take care and have a good day. 

Please click “Accepted Solution” if you feel my post solved your issue, it will help others find the solution. Click the “Kudos/Thumbs Up" on the bottom right to say “Thanks” for helping! 

Max3Aj

HP Support