Can someone identify this part please? (hall effect sensor) - Page 1
Forum section: electronics / repair

author: ceoxrad
author_rank: Regular Contributor
timestamp: March 29, 2025, 01:46:14 pm
content: Dear forum members,Does anybody know what is this part?It has 3 pins but only 2 are used, it comes from a BOSCH washing machine I-DOS automatic detergent dispenser;I searched the net quite a bit with the markings on the IC (C139 9681) but I could not find anything meaningful.The only lead I got was a product line from Allegro that kind-of matches the pinout and potentially the logic.https://www.allegromicro.com/en/products/sense/switches-and-latches/two-wire-hall-effect-switches/a1130-1-2I have reason to think the sensor is faulty because is the only active part in the detergent dispensing module, and the machine throws an error code that points to the module being faulty. I can buy a replacement module from BOSCH but is expensive and I would first try to rule out this sensor.if the sensor is similar to the Allegro one I suspect is biased by the logic board of the washer and there is some sort of current sensing being done (one side of the sensor goes to what appears to be ground in the module PCB, the other is connected to the washing machine wire harness (have not tracked that yet).Here a picture for reference.Thanks in advance to everybody!

author: fzabkar
author_rank: Super Contributor
timestamp: March 30, 2025, 12:35:48 am
content: What are the Year/Week date codes on the other ICs? That would help to determine which of the numbers could be date or batch codes. In other words, should we be looking for a part ID of C139 or 9681?Siemens uses i-Dos in their appliances:https://www.siemens-home.bsh-group.com/uk/appliances/laundrycare/i-dosInfineon was spun off from Siemens, and it manufactures sensors. Could the sensor be an Infineon part?

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 30, 2025, 03:48:12 am
content: Two-pin Hall sensors? First time I hear that!

author: wraper
author_rank: Unknown
timestamp: March 30, 2025, 03:59:11 am
content: Quote from: DavidAlfa on March 30, 2025, 03:48:12 amIt's certainly not a reed relay, you simply cannot package them in something this small. Package is like of hall sensors and magnetoresistive sensors but using just two terminals makes no sense for those. It's possible to put a phototransistor in such package but I don't recall ever seeing one like this.

author: fzabkar
author_rank: Super Contributor
timestamp: March 30, 2025, 04:05:06 am
content: Quote from: DavidAlfa on March 30, 2025, 03:48:12 amLikewise, but the datasheet explains how it works. You insert a current sensing resistor in either the high side or low side.

author: Smokey
author_rank: Super Contributor
timestamp: March 30, 2025, 04:19:45 am
content: MLX91211LUA-ABT-510-BU or variant. [?]https://www.digikey.com/en/products/detail/melexis-technologies-nv/MLX91211LUA-ABT-510-BU/16880877

author: wraper
author_rank: Unknown
timestamp: March 30, 2025, 04:41:45 am
content: Quote from: Smokey on March 30, 2025, 04:19:45 amBased on what? I don't see a single indication for this conclusion.

author: Smokey
author_rank: Super Contributor
timestamp: March 30, 2025, 07:03:13 am
content: Guess I should have put a ? at the end there. Speculation based on same package and being a hall based current sensor. Here is another.https://www.digikey.com/en/products/detail/texas-instruments/DRV5053CAQLPGM/5177930

author: wraper
author_rank: Unknown
timestamp: March 30, 2025, 07:46:12 am
content: Quote from: Smokey on March 30, 2025, 07:03:13 amThere are a lot of different Hall and magnetoresistive sensors from different manufacturers, with analog and digital outputs, different sensitivity, bipolar and unipolar, transistors and some other stuff. All in this very same TO-92S package.BTW I stumbled upon 2 pin magnetoresistive sensorhttps://www.farnell.com/datasheets/2012867.pdfmight be similar thing with but produced with middle terminal present (probably NC).

author: ceoxrad
author_rank: Regular Contributor
timestamp: March 30, 2025, 07:54:18 am
content: Thanks everybody for the insights,I add some more context.Before I made a mistake, the machine is a Siemens iQ500 (WM14UPH9/FF) and not BOSCH.The PCB of the I-DOS module is marked with text "Johnson Motor", the module appears to be this one:https://www.partsnl.nl/doseermodule-12025129/w.The sensor is surely some sort of magnetic sensor, it is placed under a gear driving the detergent pump, and the gear has some magnets embedded in it (I guess they count the turns to dispense a specific amount of detergent, so unnecessary...).Here I added a picture of the gear, there are only 2 magnets, not a ring strip magnet.I did not know about magnetoresistive sensors, the sensor reads 10M\$\Omega\$ in one direction and open in the other, regardless of a magnet being put and moved near it (measured with UT120E meter).There are no other ICs on the PCB but the injection molding of the module is dated 02/2020 and the washing machine (now discontinued) should be of similar age.It seems to be a shared part between BOSCH and SIEMENS appliances (AFAIK lower end SIEMENS washing machines are rebranded BOSCH, but I may be wrong).When the machine turns on the error is thrown after a couple of seconds (since I hear relays clicking when machine is booted I suspect it goes through some self-test at every boot).

author: wraper
author_rank: Unknown
timestamp: March 30, 2025, 08:05:05 am
content: Likely it's MLX92241LUA-BAA-1xx. Marking starting with C1 means built-in capacitor version (-1xx). The rest of marking is just lot/date code.https://www.lcsc.com/datasheet/lcsc_datasheet_2411272144_Melexis-MLX92241LUA-BAA-111-CA_C17554098.pdfImpossible to figure out sensitivity/pole version from the marking as they're not marked. But I guess you can figure out pole version from the magnet orientation.https://www.digikey.lt/en/products/filter/magnetic-sensors/switches-solid-state/565?s=N4IgTCBcDaILIBkAaBOMYAsBGBBVAggLQBC%20RWIAugL5A

author: ceoxrad
author_rank: Regular Contributor
timestamp: March 30, 2025, 08:24:57 am
content: Quote from: wraper on March 30, 2025, 08:05:05 amWow thanks a lot! this seems to match,Assuming is the right part, does this make sense?the two gear magnets are facing opposite poles so I guess pole does not matter (will be just out of phase by 180 degrees worst case)Sensitivity should not be too critical as long as it manages to release at roughly the right point in the spinIoff matters because that can be something the logic board checks to verify the sensor is operational.Direct-inverse switch may matter if the logic board does something more involved that counting edges.When the machine is switched on, it does not attempt to spin the motor of the dosing module, just throws an error. Maybe I can try measure the voltage on the sensor and put a resistor in parallel to it to fool the machine into thinking Ioff is passing, (can try different values and see if roughly matches with the datasheet).At that point perhaps the machine will attempt to spin the wheel to the point the sensor is triggered and may throw another, different error.I know for sure the motor in the module works and pump spins freely (tested with a bench PSU without the PCB connected).If that works I can just order some different revs and test them.Thanks again a lot to everyone!

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 30, 2025, 08:41:12 am
content: You could try lifting a pin, placing an ammeter and watching the current change as you attach a magnet.Maybe the issue is in the gears?

author: ceoxrad
author_rank: Regular Contributor
timestamp: March 30, 2025, 10:44:33 am
content: I tried to bias the sensor with a 9V battery and a uA meter in series (shunt resistor is ~100\$\Omega\$, so similar to the datasheet design), without magnet nearby I get 3.5mA flowing through it.This kind-of matches the 3.3mA Ioff of some of those variants, that would also narrow down to only the "direct" types, since current is low without magnet.With magnet I managed to trigger it, current reading goes above range of uA meter so the sensor works.I unfortunately don't have a lot of TE at home so today I can do very limited tests (no resistors so cannot check Ion current)Bad news is, if the sensor is good it has to be a logic board problem and I have to potentially disassemble the entire machine to get there...