Help identifying magnetic sensor SMD or equivalent for a Siemens fridge CPU

[jorgemef]

Hello,

My fridge controller board got damaged. It is a KG36VVL30S.11. Unfortunately I could not find any schematic and need help to identify one of the damaged culprits.
During repair of my siemens fridge CPU this SOT23 SMD chip with mention A26 got blown or was blown before with resistance VDD to VSS of 230 ohms.
It is a magnetic sensor chip. Anyone has idea which one it could be or an readily available replacement? The CPU triggers/latches between 2,3 and 2,6 volts and at moment I replaced it with a pull up resistor and a pull down one with external switch. It is not a fancy solution as had to glue the switch to the door hinge but works until I get the replacement.

Also I could not make the PSU work which is a flyback configuration. The burnt lnk304GN was replaced with a part purchased on a local shop but it stayed forever in a starting mode with spike every 800ms. I tested all components around from the flyback config and all seems good. All resistors are in the value. All capacitors are with low ESR (measured off the circuit).
Finally I gave up and replaced with a chinese external cheap PSU 9v 450mA and a DC-DC converter for the 5V rail until i get another chip or some other idea where to look. For now it is working with the two external parts for the power rail. Adding the schematic from the PSU reverse engineered.

Cheers,
Jorge

[fzabkar]

Allegro makes a Hall effect sensor but the "A26" marking is associated with a different package. The SOT23 package is marked A25 or A27.

https://www.allegromicro.com/-/media/files/datasheets/aps13290-aps13291-datasheet.pdf

[fzabkar]

The supply appears to be hiccuping. This usually points to an overloaded output. Did you test the HS1D diodes and 5.6V zener for leakage?

When the LNK304GN IC is regulating properly, the voltage on the FB pin should be 1.65VDC.

That said, the output voltage for the nominal 5V rail would be ...

  1.65 / 5.6 x (10 + 5.6) = 4.60V

The voltage on the BP pin should be greater than 4.85V. If BP falls below 4.85V, the MOSFET shuts off until the voltage rises to 5.8V.

Datasheet:

https://www.mouser.com/datasheet/2/328/lnk302_304-306-1512550.pdf

[floobydust]

unrelated - OP, is that PC board fuse still intact? It looks a bit nicked.
edit: the relay appears to have a 9V coil, so I would expect the SMPS output is 9VDC, then they'll run that into an LDO for the MCU etc.

[fzabkar]

edit: the relay appears to have a 9V coil, so I would expect the SMPS output is 9VDC, then they'll run that into an LDO for the MCU etc.

The OP has provided a circuit diagram:

https://www.eevblog.com/forum/repair/help-identifying-magnetic-sensor-smd-or-equivalent-for-a-siemens-fridge-cpu/?action=dlattach;attach=1682899

The PSU has two outputs, 5V and 9V.

[Traceless]

When the LNK304GN IC is regulating properly, the voltage on the FB pin should be 1.65VDC.

The LNK304GN looks like it has blown, there seems to be a hole between the "1" and the "2" on the top of the chip in the first picture.

Edit: It might also be a good idea to check on L1, GR6 (which do not seem to have visible damage) and the resistor in the bottom left corner which is either labeled R35 or R36 (the white stripe across the black band could be either superficial dirt/scratching or a crack).

[phoenixdigital]

The LNK304GN looks like it has blown, there seems to be a hole between the "1" and the "2" on the top of the chip in the first picture.

Good eye. I just repaired two boards from a washing machine with the LNK304GN (LNK364 in my case) failing. It's pretty subtle but I've got close up pics here. They have a yellowish tinge from the heatgun and conformal coating during removal. They didn't look that bad in circuit just those subtle holes and diagonal crack.

https://www.eevblog.com/forum/repair/help-identifying-parts-for-simpsons-washing-machine-mainboard/msg4618906/#msg4618906

OPs pic also seems to have the similar diagonal crack from the bottom left to top right. My circuit was similar but it's interesting that the resistor R35 (for OPs circuit) didn't fail like mine did.

jorgemef can you get a good closeup of the LNK304GN?

[Traceless]

Good eye. OPs pic also seems to have the similar diagonal crack from the bottom left to top right. My circuit was similar but it's interesting that the resistor R35 (for OPs circuit) didn't fail like mine did.

jorgemef can you get a good closeup of the LNK304GN?

Thanks, this type of PSU design seems to be used in a lot of household appliances. It is not uncommon for the Resistor (R35) and L1 to die together with the LNK304. Sometimes sometimes the damage is very obvious sometimes its not.

I think I also may have to revise my previous statement that GR6 does not show visible damage. It is hard to tell from the picture but there may be damage on that part as well (see screenshot below).

[jorgemef]

The supply appears to be hiccuping. This usually points to an overloaded output. Did you test the HS1D diodes and 5.6V zener for leakage?

When the LNK304GN IC is regulating properly, the voltage on the FB pin should be 1.65VDC.

That said, the output voltage for the nominal 5V rail would be ...

  1.65 / 5.6 x (10 + 5.6) = 4.60V

The voltage on the BP pin should be greater than 4.85V. If BP falls below 4.85V, the MOSFET shuts off until the voltage rises to 5.8V.

Hello.

Thanks for your feedback. I was not exactly sure what to expect from the operational mode of the lnk304. Since I saw some spikes coming out I thought it entered in overvoltage and shutdown for 800ms. As in the datasheet it talks about 1,6V at FB pin I thought that going about that was making the LNK304 skip the current cycle.
I tested everything except the HS1D for leakage. These I just tested with multimeter in diode mode and they seemed to have right FWD voltage.
Not sure exactly how to test for leakage? Add reverse voltage and see it it goes through? What level? Or just with some ohmmeter?

I even replaced the snubber network with a 330 ohms resistor in series with a high voltage 1nF  paralleled with a 330K resistor and all it did was making the spikes higher (9v rail spiked to 17v) so I thought the snubber network with diode and zener was ok. I used thermal camera and the DU34 was getting hotter than the other one but not much more. I thought it was absorbing more reverse energy. I could not understand which diodes these DU34 and RJ28 are, but since it also didn't worked with the other snubber network I didn't looked further.
Picture with the other snubber network for 5V rail in attachment.

After removing the magnetic sensor that was loading the 5 V circuit with 230 ohms I got attached results more flat and with more voltage but this is not regulating properly and going above the 5v required level for the CPU. Anyway 230 ohms it not that much of a load (21mA) as it needs to drive a relay which takes similar level of current and relay was not activating. It may have been enough to put the circuit closer to instability.

For the other questions, this was the initial picture with dead LNK304 and fuse resistor (22ohms) which I changed. The LNK304 was "shorted" between D and S.
I measured the L1 to 375uH instead of marked 470uH but this should not be an issue as would only affect slightly the designed EMI.
Also in the control board there is no LDO before the CPU which is a D78F0503A from Renesas. It is feed directly with the 5V rail from the regulation of the flyback. Initially I was concerned it may have gotten blown by the spikes but it hold. When I noticed no LDO I had to cut a trace with the power to the CPU to avoid damaging the CPU while testing the flyback.

Cheers,
Jorge

[fzabkar]

My understanding was that your current situation was that there was no output from your supply, and that it was hiccuping. Now you are saying that the outputs are working, but they're too high. :-?

I would examine the two resistors in the potential divider at the FB pin of the LNK304. It sounds like the upper resistor (10K) may have gone high.

If you're testing the supply without a load, perhaps you should see how it behaves after adding a load resistor across the 5V rail?

I think these are the diodes you were unsure about (I'm not sure about DU):

RS07J, Vishay, Fast Rectifier, 600V, 0.7A, marking RJ, DO-219AB:
https://www.vishay.com/docs/85742/rs07b.pdf

DZ2J056x0L, Panasonic, 5.6V zener, 200mW, for surge absorption circuit, marking DU, SC-90A:
https://pdf.datasheetcatalog.com/datasheets/panasonic/DZ2J056.pdf

[jorgemef]

Indeed I was expecting the 5V rail to not go above the 6.5V Renesas states as limit for the CPU. Damaging the CPU chip would be the end game for this board which costs 160€.

I made two additional tests. The HS1D for leakage - removed the transformer and applied 30V reverse. Not a single uA passed by, so both seems good.
The Diodes in the snubber. The mains rectifier circuit charges to sqrt(2)*220V and stays there. Then with the lnk304 out of circuit I added a resistor to ground in between the diodes and it pulls down the mains rectified voltage to 200v. So I assume one of the diodes is a 200v Zener.
I found an application on PowerIC support page which I am attaching with such a snubber in the flyback and they where using 150V zener as one of the diodes. So a 200v Zener seems OK.

I also have suspicion that the LNK304 may not be getting the feedback voltage from the feedback pin (damaged part from source?) as I see voltage there. At the moment with external supply in the 5V rail and without the LNK304 in circuit I see 1.8V on the solder path.
My next attempt will be to test the LNK304 functionality off the circuit, or purchase from another source and test with a different one.

Cheers,
Jorge

[jorgemef]

Allegro makes a Hall effect sensor but the "A26" marking is associated with a different package. The SOT23 package is marked A25 or A27.

https://www.allegromicro.com/-/media/files/datasheets/aps13290-aps13291-datasheet.pdf

I think may be this stuff. A1266ELHLX-SO3-T

Found it from this page which indicates Leed/door switches for consumer electronics:
https://www.allegromicro.com/en/applications/consumer/white-goods#pop-f7c8390a-4a7b-4478-adfc-8364c5fc1db8

Reference mentions last 3 digits of part number which would mean 266 instead of A26. Anyway the function seems to match.
Now is a mather where to find it or some alternative with horizontal detection.

BR,
Jorge

[jorgemef]

Finally parts arrived from China. Replaced the local retailer bought LNK304GN with a Aliexpress bought and now it works. 5V line and 10V line all fine. Still to understand how this happened.
Also used A3144E with a 5K resistor pull-up and works a breeze to replace the magnetic sensor. Just had to use it vertical and on the edge of the board to not mess with the led light plastic guide.

Working as new now.
Local retailer chip on the left, aliexpress on the right. Payed the same for 10 as per one local retailer and the China one is the one which works.