Disable automatic updates in the printer’s web interface immediately after downgrading, and block *.hp.com on your router for that printer’s MAC address.

If the printer loses power or the data cable is unplugged midway through the installation, the printer's motherboard can become corrupted (bricked), rendering the unit permanently unusable.

If you are in a hurry and have an urgent document to print, a temporary workaround exists. Try removing all cartridges, turning off the printer, and unplugging the power cord for 60 seconds. Then, reinstall only the cartridges that are not showing an error and print your document. Afterward, fully reinstall all cartridges and perform the official fix above.

| Issue | Likely Fix | |-------|-------------| | “Downgrade not allowed” | Printer’s bootloader is locked (newer security). Try an older downgrade file or accept that downgrade is impossible. | | Printer stuck in recovery | Power cycle, re-enter recovery, and re-run the tool with a different USB port. | | USB not detected | Use USB 2.0 port. Disable antivirus temporarily. Try another cable. | | After downgrade, still blocks cartridges | The firmware you used still has Dynamic Security. Seek an even older version (e.g., 1709A). |

HP provides an official, safe, and supported firmware update that specifically removes the Dynamic Security feature for OfficeJet Pro 8620 printers. Here’s how to do it:

Locate your HP OfficeJet Pro 8620 in the device drop-down list.