My dual FSESC 4.20 stopped working (one side only), and can not be programed - it supplies 5v fine, but 0v on the 3.3v line - and if I plug my external programmer in, the programmer shuts down (the 3.3v problem seems to be a short - which is why the programmer "gives up", because it can't supply 3.3v into the short).
The same programmer worked fine on both sides before, and works OK on the working side.
Obviously, the USB doesn't work at all on that side either.
I assume there's something that outputs a regulated 3.3v? If yes, what is it, and where? Can I replace it? (I've done SMD component replacements before).
You should not connect 3.3V from the programmer! Only original ST-links should get 3.3V connected, since that pin is a sniffer, checking if the processor is powered.
Clone ST-Links actually supply 3.3V, which can easily blow the voltage regulator or STM processor. I guess that is what happened.
CLK, IO and GND is all you need to connect.
Exactly! So - does it have a 3.3v voltage regulator? If yes - which chip is it? (I know it does not have a separate 5v regulator, because that's supplied from the DRV chip - and that's working OK anyhow).
Obviously, CLK, IO, and GND is useless right now, because there is no 3.3v on the board (and no way to supply 3.3v to the board - it "sucks up" as much 3.3v as I feel safe trying to give it - as if the broken 3.3v regulator itself is drawing the load).
The ST-Link itself "dies" when connected (stops responding to the PC's USB), no doubt owing to the fact that the VESC is drawing all the 3.3v off it. The ST-Link "comes good" again as soon as disconnected form the VESC. It works fine on the other VESC. The VESC's own USB does not show up as a USB on the PC (and again - no 3.3v power on the 3.3v pins).
So yeah... which chip is the 3.3v regulator, or, where do I look to find out?