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A
Ameni
Associate II
April 3, 2026
Solved

STM32U5G9J-DK2 – Short circuit on 3.3V, U16 overheating, LD1 off

  • April 3, 2026
  • 2 replies
  • 274 views

Hello,

I am experiencing an issue with my STM32U5G9J-DK2 board.

Description:

  • Board powered through STLINK USB

  • LED LD7 is ON

  • LED LD6 is ON

  • LED LD1 is OFF

  • I measured about 0.8 Ω between 3V3 and GND

  • Component U16 overheats a few seconds after power-up

  • No external circuit is connected

I already tried:

  • Another USB cable and power source

  • Disconnecting all external peripherals

My question:
Could someone help identify where the problem might come from?
Could U16 be defective or indicate a short circuit on the 3.3V rail?

Thank you for your help.

Best answer by mƎALLEm
@Ameni wrote:

Hello,

Thank you for your reply.

Since it is very likely an internal short circuit inside the chip, is there any test or method to confirm this with 100% certainty?

Remove JP4 to isolate the chip and measure the impedance at the MCU side using a multimeter, if it's very low in the order of few ohms this is definitly an issue. Start by using the continuity test. If with the continuity mode the speaker generates a sound it's 100% a short circuit inside the chip.

You should do the test between JP4 (MCU side- you need to find which pin of JP4) and GND with the board powered off.

2 replies

mƎALLEm
mƎALLEm
Technical Moderator
April 3, 2026

Hello,

This is a hardware issue. First thing to do is to remove JP4 to disconnect VDD from the MCU. So the chip is isolated and no more powered on. Do you face the same behavior?

If yes it's something related to power stage and could be damaged.

If no I think in this case the MCU is damaged.

But you need anyway to check the jumpers, put all the jumpers to their default position. You need to refer to the user manual of the board for that. But this needs to ensure you never modified anything on the board. Otherwise you ned to check what you've modified before the behavior to appear.

If all jumpers are set in the default position and you still having the same behavior. Most probably, and unfortunately for you, the board is broken.

 

"To give better visibility on the answered topics, please click on ""Accept as Solution"" on the reply which solved your issue or answered your question."
    A
    AmeniAuthor
    Associate II
    April 6, 2026

    Hello,

    Thank you for your suggestion.

    I removed JP4 to disconnect VDD from the microcontroller. After removing JP4, the short circuit between 3V3 and GND is no longer present, and the overheating issue disappears.

    It seems that the problem only occurs when the microcontroller is connected to the power supply.

    Does this mean that the microcontroller is damaged?

    Thank you for your support.

    mƎALLEm
    mƎALLEm
    Technical Moderator
    April 6, 2026
    @Ameni wrote:

    Does this mean that the microcontroller is damaged?

     

     Most probably and unfortunately for you .. yes. Most probably a short circuit inside the chip.

    "To give better visibility on the answered topics, please click on ""Accept as Solution"" on the reply which solved your issue or answered your question."
    TDK
    TDK
    Super User
    April 4, 2026

    If U16 is the LDO, it's expected that it heats up if there's a short somewhere.

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