St Link v2 connection

[Banabender]

I´ve bought a new ST-Link V2 from a reputable electronics Vendor (Reichelt, Germany) to connect to my Cartographer 3d scanner for a 3d Printer with an stm STM32 chip. It is connected correctly as far as I know. I cannot establish any connection. I've also tried another board that didn't get recognized, so I think my ST-Link is broken, or am I overlooking something here? They both sometimes show as SN: 31FF710631315436290343, but as soon as I try to connect they just vanish. Is the ST-Link broken, or am I missing something since this is my first time doing this?

[Karl Yamashita]

Try another USB cable and/or another USB port. Are either boards powered up while you're trying to connect the ST-Link? Are you using STM32CubeProgrammer? Are there no error messages of some sort?

Show the a diagram on how you've connected the ST-Link to the 3D scanner board and it's pinouts. 

[Tesla DeLorean]

Pin 1 of the ST-LINK 20-pin header needs to be 3.3V or the Voltage of the Target, it's an input to the ST-LINK to power the interface to your board.

You really shouldn't be powering the board from the ST-LINK (Pin 19?)

You need a common ground, but the 3V3 from the board should be going to Pin 1 of the ST-LINK

Other connections SWDIO, SWCLK, NRESET