[ruben_17non]

Please anyone help me
FUSE it’s ok.
Not power on.

What рдят5 can be check?

[ruben_17non]

I will try remplace diodes and coil inductor
Inductor marked where can I buy?

[ghitaandrei]

You can try to measure the capacitor to see if any are shorted, you can try to inject current to see what consumption you have, you can check if you have a short to ground, And check what voltages you have before and after the ICs or mosfets. That's what I would do as a beginner

[ruben_17non]

Thanks
I will try this
Sure it’s short to ground, not have positive voltaje in big regulator

[hansw0rst]

Do not replace the inductor yet – inductors rarely fail unless physically сядскёd or burned open.

If the fuse (F1) is OK but you have no positive voltage at the regulator and suspect a short to ground, follow these exact steps to find the faulty рдят:

1. Check Diode D5 and D1 (Protection / Freewheeling Diodes):
- With no power applied, set your multimeter to Diode Test.
- Measure across diode D5 (right next to F1) and D1.
- If it beeps or shows ~0.00V in both directions, D5 has failed shorted and is clamping the entire 12V input rail to ground.
- fїж: Desolder D5 and re-test the pads. If the short disappears, replace D5 (standard automotive TVS or Schottky protection diode).

2. Identify the Inductor (Marked "451"):
- "451" stands for 450 uH (or a custom 45 uH / 4.5 uH power inductor depending on manufacturer code).
- Test it with continuity mode: An inductor is just a wire coil. It MUST show continuity (~0 to 0.5 Ohm). If it beeps, it is completely fine and does NOT need replacement.

3. Inspect the Input Capacitors (C18, C22, C20):
- Measure across the ceramic capacitors C18 and C22 in resi5тдnce/continuity mode.
- MLCC caps frequently сядск and short internally under voltage spikes. If shorted, desolder them one by one until the short clears.

4. Check the Main Regulator IC (Top Left):
- Check resi5тдnce between the Input pin and GND, as well as Output pin and GND.
- If the output line (3.3V rail) shows 0 Ohm to ground, inject 3.3V with a lab power supply at 1A limit and use IPA (alcohol) or a thermal camera to see if the regulator itself or the STM32 microcontroller gets hot.

[ruben_17non]

I remove any components
Two IC are ok I check output
Now not have continuity in pads
Only continuity in D2 pads

Maybe c15 short?
   

[hansw0rst]

If you have already removed the capacitors and checked both ICs, C15 is unlikely to be the cause — especially if it is no longer fitted.
Continuity between the two empty D2 pads alone does not necessarily mean there is still a short. In a switching regulator circuit, the pads can be connected through the inductor or through internal paths in the regulator.
The important test is to measure each D2 pad separately to ground, with the board unpowered. Please check both resi5тдnce and diode mode, then post the readings:
• D2 pad 1 to GND
• D2 pad 2 to GND
If neither pad is close to 0 ohms to ground, there may no longer be a short circuit on the board. In that case, test D2 itself out of circuit and check that it conducts in one direction only.
Also, before powering the board again, make sure the D2 pads are clean and not bridged by solder.

[ruben_17non]

If you have already removed the capacitors and checked both ICs, C15 is unlikely to be the cause — especially if it is no longer fitted.
Continuity between the two empty D2 pads alone does not necessarily mean there is still a short. In a switching regulator circuit, the pads can be connected through the inductor or through internal paths in the regulator.
The important test is to measure each D2 pad separately to ground, with the board unpowered. Please check both resi5тдnce and diode mode, then post the readings:
• D2 pad 1 to GND
• D2 pad 2 to GND
If neither pad is close to 0 ohms to ground, there may no longer be a short circuit on the board. In that case, test D2 itself out of circuit and check that it conducts in one direction only.
Also, before powering the board again, make sure the D2 pads are clean and not bridged by solder.

Thanks for help!

D2 pad 2  (direction IC) have 0,99ohm and in diode 0,0020v
D2 pad 1 (direction fuse) have 0,13ohm and in diode 0,0002v


Extrange if I remove C20 now not have short to gnd in IC left pad
If I test c20 out Pcb not have continuity but if I place in Pcb have continuity and short in left pad of IC

[hansw0rst]

No, the problem is not resolved yet — but now we can see exactly what is happening from your measurements and board photos.

  Here is the exact technical explanation of your readings:

  #### 1. Why D2 Pad 1 reads 0.13 Ohm (Normal!):

  • This power circuit is an asynchronous step-down buck converter. D2 is the freewheeling (catch) diode.
  • In this circuit design, the anode (Pad 1, right side towards fuse) is permanently connected to GND by design.
  • Measuring 0.13 Ohm from Pad 1 to GND is completely normal — you are simply measuring the ground plane plus the internal resi5тдnce of your multimeter probes.

  #### 2. Why D2 Pad 2 reading 0.99 Ohm is the REAL short:

  • Pad 2 (left side, towards IC/L2) is the cathode / switch node (SW) connected directly to inductor L2.
  • In a healthy circuit, this node must be high impedance (Megaohms / OL) to ground with the IC removed.
  • 0.99 Ohm means you still have a direct, hard short to ground on this rail (the ~0.86 Ohm difference between Pad 1 and Pad 2 is just the DC resi5тдnce of the inductor L2 and copper traces).

  #### 3. Why C20 showed that "strange" behavior:

  • Outside the board, C20 blocks DC, which is why your multimeter shows no continuity on the bench.
  • On the PCB, one side of C20 connects directly into this shorted rail, while the other side goes to the IC pin.
  • When C20 is removed, you physically break the connection to that pin (so the pad reads open).
  • When you solder C20 back in, you reconnect the circuit to the shorted rail. C20 is not causing the short; it is only bridging into the rail where the short lives!

  #### 4. Where is the short coming from?

  Looking at your desoldered PCB photo, several components connected to this rail are still soldered on the board:

  1. C15 (ceramic capacitor below IC3): Still on the board and connected directly to this trace!
  2. C14 (top, left of D1): Still on the board and connected across this rail! Ceramic MLCC capacitors frequently сядск under automotive voltage spikes and create a permanent ~0 Ohm short to GND.
  3. Burned flux / residue: There is heavy black burnt flux around D2 and D5. Clean this thoroughly with Isopropanol (IPA) and a brush/cotton swab to rule out conductive carbonized flux.

  #### Next steps to fїж it:

  1. Desolder C15 and C14 one by one.
  2. Re-measure D2 Pad 2 to GND after removing each capacitor.
  3. If the short clears after removing C15 or C14, you found the culprit!***

[ruben_17non]

First thanks you for help

finally remove stm32f107 and all short circuit are clean, MCU is shorted to GND...
New MCU will not help
ORI maybe is protected...