HOW DO I un-lock the scanner on a Brother MFC 7420?

Unfortunately, the MFC-7420 doesn't have a physical lock switch. You need to turn off the all-in-one and wait for the unit to clear its memory. If the error recurs after you press the power button again, wait 30 minutes and try again. (Note: you will lose any faxes that are in memory. See the User Guide page 11-5 to save this information.) You can find the manual on the Brother support page for the MFC-7420: https://www.brother-usa.com/support/ModelInfo.aspx?R3ModelID=MFC7420 . Click on the Manuals & Documents tab. Then click on the Manuals on our Online Solution Center for the English version of the manual. The direct link to the User Guide is currently: http://download.brother.com/welcome/doc000387/ALLFB_UsaEngUsr_B.pdf .

You can also try unplugging the all-in-one for several minutes to reset the error codes. If the error persists, contact Brother if the MFC-7420 is still under warranty (1 year). If it isn't under warranty, consider replacing the unit. The repair costs may be unreasonable.

I hope this helps.

Cindy Wells