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How to fix VESC killed by over current in serial comm?

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8bit
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How to fix VESC killed by over current in serial comm?

Hi,

I have two flipsky VESC 6.6 (https://flipsky.net/collections/electronic-products/products/fs-esc-6-6) that I think was killed by over current into the RX/TX pins. The VESC was connected to an arduino, which has a complicated and dasiy chained path to common ground with the VESC. I did not have a grounding pin between the VESC and the arduino. When I accidentally turned the power switch off, I think that somehow caused a voltage differential between the arduino and VESC that caused an excessive amount of current to flow through the Arduino and VESC RX/TX pins (both the arduino and the vesc died). 

Looking in the schematic, it looks like the TX/RX pins go directly into the STM32. Am I correct to assume the STM32 is dead? Am I correct to expect that this should be fixable by replacing the STM32 chip (and flashing firmware on it)?

ncer
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I think your suppose is right, and you need to replace a new stm32 chip.

On the other hand, you should never connect the uart interface without common ground.

vadicus
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If both are dead, chances are the MCU is a toast. It's easy to check by trying to reprogram the MCU via the SWD (without connecting the main battery). If it takes the program and LEDs come alive, it may be good but the power supply is shot. Can be both. 

8bit
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Thanks guys, I figured the stm32 is gone. Guess I will have to wait till they come back in stock to try a fix.

neo
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Check the 3.3v rail, those regulators do not like to be backfed with voltage, you may be lucky and only need to swap it out.

Power it and check any of the 3.3v pins, if you get nothing externally inject some power and see if you get signs of life.

Had a few flight controllers go this way from loose connections, worth checking the vin pin for said voltage, directly on the mcu as could even have fried a diode 

Image to the left shows the regulators,with the three pins at the top, the bottom right is the 3.3v output.

Good luck!