Hi @WizardBob,
Welcome to HP Support Community.
Thank you for posting your query, I will be glad to help you.
If your HP OfficeJet Pro 7740 printer is displaying an error message stating that the printhead is not installed, even after you've removed and reinstalled it multiple times, there could be a few potential reasons for this issue:
Printhead Contacts: Ensure that the contacts on the printhead and the printer carriage are clean and free from any dust or debris. Use a lint-free cloth lightly dampened with water to gently wipe the contacts.
Printer Firmware: Check if there's a firmware update available for your printer. Sometimes, updating the printer's firmware can resolve compatibility issues and improve performance. You can usually check for firmware updates through the printer's control panel menu or the HP website.
Printhead Connection: Double-check that the printhead is securely seated in the printer carriage and that it snaps into place properly. Sometimes, a loose connection can cause the printer to not detect the printhead.
Electrical Contacts: Inspect the electrical contacts on both the printhead and the printer carriage for any damage. If any of the contacts appear damaged or bent, it may prevent the printer from detecting the printhead properly.
Reset Printer: Try performing a hard reset on the printer. To do this, turn off the printer, disconnect the power cord, and wait for about 1-2 minutes. Then reconnect the power cord and turn the printer back on.
I hope this helps.
Take care and have a good day.
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Rachel571
HP Support