ST‑LINK Mini V3E not detecting STM32H7 (Core ID error, high current when VTARGET connected)

[AEng7]

ST‑LINK Mini V3E not detecting STM32H7 (Core ID error, high current when VTARGET connected)

I’m debugging an issue with a custom STM32H7 board and an ST‑LINK Mini V3E. The setup includes a main PCB and a separate power PCB. So far:

Power & Basic Checks

• 3.3 V and 24 V rails are correct.

• Board current consumption is low when powered from either an 8 V or 24 V supply.

• Connections between the ST‑LINK Mini V3E and the main PCB have been verified.

Problem

• When I connect VTARGET from the ST‑LINK to the board’s 3.3 V rail, the current spikes and something starts to smell hot.

• STM32CubeProgrammer shows no target voltage, no device ID, and fails to read the core ID.

• The ST‑LINK is detected by the PC normally.

Additional Tests

• Tried a second main PCB and a different ST‑LINK Mini V3E, powering only through the ST‑LINK (no external supply). Same result: STM32CubeProgrammer cannot detect the STM32H7.

• I’m aware that VTARGET on the Mini V3E is an input, so I’ve tied it to the board’s 3.3 V rail as required.

Next Steps I Plan to Try

• Measure resistance between 3.3 V and GND to check for shorts.

• On PCB #1, pull BOOT0 high with a 10 kΩ resistor (removing the existing 10 kΩ) to see if the MCU becomes detectable.

• Re‑verify grounding between the PC, ST‑LINK, and the board.

• Try a different ST‑LINK model (non‑Mini).

•  

[TDK]

Sounds like the grounds are not connected. Connecting 3.3V to the vtarget input would not cause issues. Something is miswired, hard to know what without seeing the setup.

With everything else connected, take a multimeter and measure between gnd on the programmer and 3.3v on the device.

[AEng7]

I would have thought connecting the GND from ST-Link via the programming pins to the programming header on my custom PCB would ensure they would share the same common ground. 
I will double check if they are connected, and report back. Thank you!

Without the programmer connected, current consumption is as expected and voltage rails are as expected. 

[AEng7]

I also don’t have a LTDC 24bit RGB LCD screen connected to the custom PCB so wondering if leaving that unterminated is also contributing to this.

 

Additionally, I tried soldering some wires from the STLink to the custom PCB programming pins, and the current consumption only shoots up when the v target pin is connected, without it the current consumption is normal 

Ill report back on Monday 

[TDK]

Connecting grounds will ensure they have a common ground. But connecting vtarget under such a scenario will not cause current to spike. So something is different from what you are describing. The task is to find out what that is. Since the programmer responds, it’s unlikely that the programmer is damaged.

[AEng7]

After fault finding/troubleshooting turns out custom board #1 was damaged which I believe was due tk me potentially plugging the programming incorrectly.

 

The rest of the custom boards program fine.

 

Thanks for the help!