There’s not much of a circuit. The 5 volt track to the motor driver chip needs to be cut, then cleaned each side of the cut.
Then I soldered a wire to the track each side of the cut.
The wire nearest the driver chip is then connected either to:
– the original 5v line (the other wire), for normal operation.
– a 9volt supply. For faster motors.
I will post an image of which track to cut.