I have stm32f407vg discovery board. I could program my board successfully before but now my pc can't recognize debugger. What should I do to fix it?

[TDK]

Undo what you did to make it stop working.

[kb24]

I dont know what caused this, actually I have a guess. I touched the debugger and led turned off. So static might caused this. Any suggestion?

[TDK]

ESD can definitely kill things. If it's a ST board, and the computer can't recognize the debugger after a reset, I would guess it's dead. Although that would be uncommon. Does it show up as connected in the device manager? Does the board have the correct voltage level? Not sure if the LED is tied directly to power or not, but you could check that in the schematic to help diagnose.

[kb24]

I have discovery board.

Device manager says unknown usb device (device identifier operation failed). On 5 V pin I measured 4.78 V and 3V pin 2.99 V.

Led that turned off is COM led.

[TDK]

If COM is neither red nor green and your chip has power, then likely your onboard ST-Link chip is fried. The actual MCU might be fine.

[kb24]

So is there any way to fix it or it is dead?

[TDK]

Assuming that's the problem, the ST-Link chip is dead.
You can still connect to the MCU chip if you have another ST-Link available. You need the NRST, SWDIO and SWCLK lines connected.
Probably easier to buy a new board though.

[kb24]

Okay. Thanks.