Polarity reversed connection of the battery is the most common incident happend with the BETAFPV FC boards or BNF drones. It result a permanent damage on the FC board in hardware. As a result, the FC board or the drone will perform like one of the situations blow.
Situation 1): Works well when USB cables and battery connected at the same time. But only the battery is connected, the receiver LED is not light ( for FC boards with native receiver integrated) and could not connect to the radio transmitter, could not arm, no video ( if video in and out connected). Here is the description about this issue( from customer).
but the osd/video feed do not work until plugged into usb power.
It seems like there's enough power from the battery to make the green lights flash but not enough to power anything else.
cannot get it working without connection to USB.
It seems that controller cannot even connect to radio if I unplug USB cable, nothing happens, led lights are not blinking, but when connected controller is fully functional: all channels work as expected, I can see this on Receiver tab in Betaflight configurator. Moreover when I plug in the battery, if I turn Throttle up motors are spinning.
Situation 2): Motors stop sipping up when throttle up. The drone is flying like frog jumper. Here is the description about this issue( from customer).
My problem is that my transmitter loses connectivity to the receiver at greater than 50% power....this of course kills the motors to the quad.
When checking the settings in Betaflight GUI, everything seems work well.
When land on the ground, the connection and bind work well.
When the motors start to spin, the drone keeps loosing bind during flight.
How to Inspect
1) If you are in the situation 1, check the red receiver LED when only battery or USB cable plugs in. If the LED is light only when USB cable pluged in, wow, damaged.
2) If you have a multimeter in hand, you could check the ouput voltage of location according to the images below. The voltage of the position at the arrow pointed to should at least 4.1V. If the voltage is below than 4V, that means the FC board is damaged.
For F3 EVO FC with Frsky Rx, plese circle and negative on battery ground.
How to Fix
Battery connects polarity reversed will result a permanent damage on the voltage conversion IC and please contact us to get a new replacement. Please send email to "firstname.lastname@example.org".
Of course, if you are able to replace the set up converter IC, it is SDB628 from SHOUDING. Here is the datasheet for it.