I just bought a working BMR104 off Gumtree . Everything great until I plugged my phone into the aux input then the display went blank.
Here is my fix .. real weird, but it worked:
Switch on radio
Press Advanced button once
Press the volume/tuning knob once
Carefully rotate knob clockwise 6 clicks
Press knob once
Rotate knob clockwise 1 click
Press knob once
Wait. Radio now resets and retunes but display remains blank.
Switch off radio and back on.
Repeat the above procedure.
This time after resetting, the display springs into life and says something like “WAITING FOR PC WIZARD”
Switch off radio
Connect a PC to the micro USB socket
Switch on the radio, the display should now work.
CAREFUL! I repeated the fault by plugging my phone into the AUX jack again. The same process did not work a second time on the same PC USB port, but did work when plugged into a different USB port ... something to do with loading drivers??
Anyway see if it works for you
Phil W80, January 2020