HP8740 ADF Sensors

[johnnyorwell]

Recently replaced the glass flatbed in my 8740 scanner but am now having sensor issues with the auto document feeder (ADF).  I had attempted to take apart the ADF to clean it but a gloomy concern came over going too deep and not being able to find my way back.  I put it back together and now I can’t get the ADF to sense any paper.  There appear to be two switches that interact with visual sensors when the switches engage and the document detection message shows up on the printer screen.  The first switch, which is supposed to trigger detection before paper is fed in, is what won’t trigger detection here.  The second one, which triggers as paper is being fed in does work.  See images below.

 

 

[Sneha_01]

Hi @johnnyorwell,

Welcome to HP Support Community.

Thank you for posting your query, I will be glad to help you.

It sounds like you've encountered a common issue with the Auto Document Feeder (ADF) after working on your HP OfficeJet Pro 8740. Here’s a step-by-step guide to help you troubleshoot and potentially fix the problem:

1. Check the ADF Paper Sensor Switches

• Locate the Switches: Confirm the location of the two switches you mentioned. Typically, one switch is for detecting the presence of paper before it is fed, and the other is for detecting paper during feeding.
• Inspect the Switches: Ensure that the switches are correctly aligned and seated in their positions. Sometimes, if a switch is slightly out of place, it may not trigger properly.

2. Clean the Sensors and Switches

• Turn Off the Printer: Make sure the printer is powered off and unplugged.
• Clean the Sensors: Use a soft, lint-free cloth or a cotton swab lightly dampened with isopropyl alcohol to gently clean the sensors and switches. Avoid using excessive liquid, as it can damage the components.
• Dry Thoroughly: Allow any cleaned areas to dry completely before reassembling.

3. Check the Sensor Mechanism

• Ensure Proper Alignment: Verify that the mechanism that triggers the switches (like paper trays or levers) is properly aligned and moving freely. Sometimes, reassembly can cause misalignment.
• Test the Switches: With the printer off, manually press the switches to ensure they are functioning correctly. You should hear or feel a click if they are working properly.

4. Reassemble the ADF

• Careful Reassembly: Reassemble the ADF carefully, making sure not to force any parts into place. Ensure all components are correctly aligned and seated.
• Check for Obstructions: Ensure that no small pieces or foreign objects are obstructing the sensor or paper path.

5. Perform a Test Scan

• Turn On the Printer: Power the printer back on.
• Test the ADF: Try scanning a document using the ADF to see if the issue has been resolved.

6. Check Printer Firmware

• Update Firmware: Sometimes, updating the printer’s firmware can resolve hardware issues. Go to HP's support website, find your printer model, and check for any available firmware updates.

I hope this helps.

Take care and have a good day.

Please mark this post as “Accepted Solution” if the issue is resolved and if you feel this reply was helpful click “Yes”.

Rachel571

HP Support

[johnnyorwell]

I put in a replacement ADF.  I can’t figure out why the original sensor has failed.  But the replacement works.  Now it seems the paper won’t feed through the ADF completely or there’s no way to test it without putting the upper and lower halves of the scanner back together.

[Sneha_01]

Hi @johnnyorwell 

I'm sending out a private message to assist you with the next course of action. In order to access your private messages, click the private message icon on the upper right corner of your HP Support Community profile, next to your profile Name.

Hope this helps! Keep me posted for further assistance.

Please mark this post as “Accepted Solution” if the issue is resolved and if you feel this reply was helpful click “Yes”.

Rachel571 

HP Support