Can't find SMD marking code

[taar]

Hello
This is my first post on this forum. So hello to everyone and thank You all for any help You can provide.
My problem is that I can not find this SMD marking. Marking is 403 HE. Component is shorted. This is Grundfos pump controller board. As You can see on other picture choke component heated and inductor after choke is burned. This unknown component (some diode) is down in line.

Thank You

[bigendian]

it may be a schottky diode considering the polarity. Did you desoldered ? If not, solder it down to be sure it's shorted.
Can you measure the other with diode probe and report the value ? 0,2 about in one sense is a schottky

[taar]

I removed it from board and it is shorted. I desoldered another one from board that works and voltage drop is 0.67V and reverse current is 2.8uA. This burned component, could it be limiting resistor for buck regulator? This line is connected to Vin of buck regulator and voltage is 28V before burned part. Regulator is LMR14003

[bigendian]

I don't think a resistor, they have not that package in any case, and since there is a polarity.
If you measure 0.67 by diode probe, it is a normal diode. But it seems to  me a schottky diode. Are you measuring it by diode probe symbol of the tester ?
And maybe is a protection diode to avoid inverse polarity. If you can draw down a schematic of that part, it would help.

[taar]

Sorry I meant this other picture where You can see burnt marks on PCB. This white 4 pin part is choke and after it in line before capacitor is burned part. Can not tell if it is a resistor or inductor. Rest of board have few similar parts that are resistors (same size as this burned part) without markings and inductors, but inductors are little bit larger than this burned part.
I measured diode with multimeter on diode symbol and with Fnirsi  component tester.

[bigendian]

ok sorry for misunderstanding so.

What is the in voltage you expect to have ? Do that "in voltage" goes to the near IC Vcc ? What is that IC ? Likely, that was a fuse resistor, or a protection diode as a schottky, or, a bridge, or a small resistor. You could probably be able to measure voltage at that choke output. If is the same to be expected as Vcc of the followinig IC, that was probably a fuse. I would probably use a fuse there at least for test, so if there are other parts after it in short, it burns

[taar]

Voltage of 28V that I have on choke (on both sides) goes to this burnt part. After that it goes to Vcc of voltage regulator (LMR14003) that can take voltages from 4 to 40 V and converts it to 5v. I don't have any dc fuses at this moment.
 I connected resistor fuse, but still don't have voltage over part of board. I removed choke and wire that goes to one of 4 legs is broken. I need to find another choke and replace it for start.

[bigendian]

Ok-

I am supposing something at valley side, likely components powered from LMR14003, or LMR14003 itself, has caused that fuse/resistor to burn.
Maybe that MCU or some driver just around it.

Choke on DC lines is just something you can short for test, if you think is damaged.
So i would first check carefully the smd electrolytic capacitor near the burned part, that is not in short.

Then, a technique is to provide yourself the 28V with a bank supply, limiting current, starting from few mA, and checking by hand if some component get really hot with a very fast touch on the body. That is generally the faulty component caused the fault of the fuse.

Another old technique is to connect a 220V lamp in serie to the main power supply, in cases of short, voltage fall on the lamp will save the board.
 

[TimNJ]

The manufacturer logo is Diodes Inc. Asked ChatGPT for diodes with "HE" marking in SMA package, gave me the wrong answer (DDZ9686), but that at least pointed me towards a Zener diode. Perused the Diodes Inc Website for zeners/TVSs in SMA package. It looks like it is probably SMAJ5.0A-13-F.

Between what two nets/nodes is this diode connected between on your board? Use that information to determine whether a zener is plausible in this location.

[bigendian]

Good catch, SMAJ5.0A-13-F. is not a zener, but an unidirectional voltage protector, kind of zenamic. they generally shorts with overvoltages.. Can be, sure.

[inse]

This might become a tricky case…
The choke has died from a massive surge as you can see from the vaporized and condensed copper, this does not happen from simple overload.
Either there was surge on the mains line or another component that was meant to isolate the low voltage circuit from the mains voltage failed and thus a loop has formed that allowed a massive surge to destroy the common mode choke and the small component.
So probably components on the low voltage side might be damaged as well.
As you mentioned you have a functioning board, it would help to identify the small roasted component.
I could imagine it was a chip bead for filtering, for testing you can bridge both parts but I would include something to prevent further damage like a fuse or a light bulb in series.

[bigendian]

Ah, ok, similar to a lightning so. Yes, surprises here and there are possible so., even resistor values altered.

[taar]

Thank You all for your answers.  I have 3 boards with same fault so no way to determine this burnt part. But it could be fuse resistor. I have 4 diodes per board and on every board 2 of 4 diodes are in short. Diodes are connected to PTC temperature probes. One of them is on other side of board.
I removed working diodes from one board and put them on another board. After that there is no short. Found (on different PCB) resistor 0.3ohm and put it on place where burnt part is.
I removed damaged choke and connected bench power supply on that place.  Voltage is set at 28V and current 100mA.
Turned on power and there is 30mA of current, on thermal camera max temperature of components on this part of board is 27Celsius. Led light on board turns on and seems everything works.
After that I connected this part of board to the rest (bridged terminals where choke was connected).  Turned on and board lights up. No overheating (max temp. on board is 30Celsius).
Now when measure voltage on PTC probes, voltage goes from 1 to 5V. When turned on with probes connected, it works. When I disconnect probes there is error on display, but when connected again error won't reset unless I turn OFF and ON device. It could be problem with IC (D70F4182)
Thank You TimNJ and bigendian for diode. I will order new TVS diodes and inductors.

[fzabkar]

Now when measure voltage on PTC probes, voltage goes from 1 to 5V. When turned on with probes connected, it works. When I disconnect probes there is error on display, but when connected again error won't reset unless I turn OFF and ON device. It could be problem with IC (D70F4182)

ISTM that is normal operation.

[taar]

Just tested probes and it goes to alarm when temperature reaches around 55Celsius. So it seems that is normal operation. Thing is that I should be able to reset error when everything is back to normal 

[bigendian]

That D70F4182 seems a custom/asic microcontroller, with internal flash/program. Let's hope it is all ok.

[inse]

Are all the pumps from your house and did they fail simultaneously?

[taar]

I hope too that IC is good
I don't know if they are from same place (friend brought them to me to see if I can fix them). Could this happen if temp sensor is shorted? Because if there is high voltage on this part of board there should be more damage.

[inse]

Did you get the thing running again?