Have a weird one, a V10 Motor PCB that will not work in low or medium speed (just pulses once for like 1/4 a sec and gives up), in Max mode it runs, but appears to be a tad slow (scoping the hall-effect output, I see 6.8kHz instead of 7.3kHz on 2 other working PCBs I have, on the same motor).
So far I've figured out the following.
U7 and it's vicinity are a ~10V buck converter, that voltage is present and stable even after the motor is commanded off with the trigger depressed.
U10/J8 vicinity are the battery data lines (differential pair I presume).
U4 on the bottom side is the motor hall effect sensor, that same signal is brought out to a test point on the top edge of the board. I have tried swapping in a known good hall effect sensor with no change in behavior.
U2 is the 3/3V regulator that supplies the main uC, the speed selector and U4 at least, that voltage is also present and stable after the motor is commanded off with the trigger depressed.
What I haven't worked out, is what's tripping the uC to cut drive to the motor, the FETs are not shorted, FET drivers on the top side appear to work properly when scoped.
Additionally I tried shorting out the shunt resistor on the bottom side of the board, the PCB will refuse to drive the motor, which is weird (unless the uC is using the current waveform to drive the motor perhaps).
What I have yet to do is to extend the motor and hall effect (U4) sensor wires and do some probing around the bottom side of the board.