Warning for Rev0.1! Be careful when soldering C42 and C43 - they should not be in contact!

The 1st pin is marked with a little dash:

Now check if MCU works using ST-Link/V2 programmer:

Make sure that an external +12V power supply is always connected when using the board:

The programmer connector pinout (from left to right): 1 - the first pin is not used 2 - GND (ground) 3 - NRST (reset) 4 - SWCLK 5 - SWDIO