4XX - 4XXX Brush motor MOSFET
If your brush motor will run when connected to a Roomba battery or 9 volt battery but won't run when connected to the Roomba main PCA
then it may be due to a U11 circuit device failure. On most of the circuit boards used today there is an additional location next to the U11 circuit that you can install a heftier MOSFET to run
that brush motor
You can order a replacement MOSFET by selecting the paypal button below.