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help with ST link

Associate III

i have a blue EVAL board (STM32H735G-DK) that I think stopped working.

There is a ST-com LED that starts green but changes to RED and stays that way. The driver shows up on COM 3 in device manger. The STM32CubeIDE that I use does this at time but this time its not finding it.

Target no device found
Error in initializing ST-LINK device.

I also tried STM32Cube Programmer but never used this before. It seems not to find it either. I'm sure its ok as it comes up and runs fine and installs a driver. I just have no info and how to troubles shoot this. Could the com port change, is that set somewhere in the IDE?Did I bump a jumper? This is windows 11.


If I reboot the ST-link com lights blinks and goes green. But still no luck programming. If I unplug the USB and plug it back in the light stays red.

Chief II

This board isnt simple Nucleo, you can reconfig it to complete dont work usw.

Is your micro USB cable OK? Check it as first. And continue with learn howto use sw and ...

Associate III

I also have a white board Nucleo, I tested it with the same cable and it works. I think maybe the blue board has a problem but unsure what. The power config says ST.


Associate III

"The LD5 green LED turns ON when the voltage on the power line marked 5V is present. " its Red... and I checked a few points, there is no 5v..Maybe the 5v regulator is bad? I could supply it from another place for a test but not sure that is wise.


I also see this "6.2.1 Supplying the board through the STLINK-V3E USB port: 5 V/500 mA" section. It is set to STLK I can try usbfs.


this gives me interesting results. If I plug in the CN14 first, then CN15, unplug CN15 and plug it back in, I get two green lights.

If I plug in the CN14 first, then CN15,   I get a green 5v light and a red ST com light


Neither mode works.



Have you checked the jumpers for the power supplies?

Anyway, LD5 is a green LED (on my STM32H735-DK board), that cannot be red.
LD5 is on when the jumper on JP7 is set to the right to STLK and the STLK USB is plugged in.

I'd rather trust the board's schematics, which you can download as a pdf ... somewhere, should be *MB1520*.pdf .

Associate III

setting to STLK  give the red light and no 5v. but setting to fsusb  and using a cable to cn14 works. But in both cases I can not program.

with the fsusb I get this


if the board ST link is burned out, can I use an external st0-link to program? If I remember right it has a jtag on it, I see the foot print of a jtag on this board.

from the schematic.

u11 has 3.2v out
CN5 pin 5= 5v
CN5 pin 4 = nothing

u17 5V in , nothing out. Sadly I do not have this chip, and it look like a tricky one. How much harm in making a 3v3 jump?

I see the blue board has a ST1L05APU33R
and the white a ST1L05CPU33R

they look the same for the most part



... and the schematics must be read correctly (by me!):

- STlink is supplied as soon as you plug-in the STLK-USB, the USB 5V "5V_USB_CHGR" go via a diode to the 3.3V LDO for the STlink MCU, if nothing else happens, the STlink MCU turns LD6 red

- JP7 sets the input voltage "5V" for the 3.3V LDO which supplies the STM32H735 and connected components. As soon as the 5V are supplied, the green LD5 turns on.

- red LD3 only turns on when the USB 5V switch U23 (input: "5V_USB_CHGR" 5V from USB-STLK, output "5V_USB_STLK") shows an error, but only if the jumper on JP7 is set to pins 1-2. If that is so, then there might be some short circuit at "5V", which is supported by the fact that green LD5 is off.

So look for some short circuit at the "5V" node.

Chief II

You use connect under reset mode ?


u17 5V in , nothing out. Sadly I do not have this chip, and it look like a tricky one. How much harm in making a 3v3 jump?

Yes, ugly DFN6 package. But at least the 5V get to that LDO.

setting to STLK  give the red light and no 5v

So that switch U23 turns off at too much current, there is a short circuit somewhere... 

But maybe the LDO is okay and there's a short circuit at the "3V3" for the H7 - which will be terribly hard to find, because that voltage goes everywhere...
So I would turn power off and check the closest capacitors for short circuits.

> How much harm in making a 3v3 jump?

I don't know what you mean, but as long as there's some short circuit somewhere, don't do it! 😉 

> I see the blue board has a ST1L05APU33R and the white a ST1L05CPU33R

Better check the datasheet!


I was curious and just checked the datasheet:

ST1L05APU33R / ST1L05CPU33R: completely different pinout!

Wow, I hate that! Bad design, in my opinion, same IC name except for one suffix letter...