I'm using my MB 5120 printer over WiFi from a Windows 10 laptop. As soon as I turn on the printer it goes into fax mode. I can't STOP it or turn the machine off. I can pull the power plug, but as soon as it starts it tries to print to the fax. I don't use fax and would just as soon disable the fax if I could.
I have made the printer my default printer. I have removed the default fax device from the list of printers & scanners. If this keeps up I will have to return the machine as defective and try to get my money back.