Hall effect sensor identification and test

[gaminn]

Hi,
LEM HY50-P/SP1 +- 50A current transducer failed in a device, and it is impossible to buy it or find a replacement. I disassembled the sensor and removed the hall effect sensor. Any idea about part number of the hall effect sensor or pinout of it? I would like to test it whether it failed

[dmendesf]

4 wires usually means a hall bridge (like 4 resistors). No idea about the PN.

[gaminn]

Yes, you are right, there is either 730 or 1000 ohm resistance between each pin pair.

[gaminn]

I was able to repair the failed sensor. Desoldered hall effect sensor, opamp, checked diode and transistor and believe it or not, several SMD 0603 resistors had resistance different to its marking or they were open circuit. I don't understand how resistors and no semiconductor can fail. They must have used some really low quality product back then when they manufactured the sensor.

[gaminn]

I was able to repair all the sensors by replacing all 0603 resistors with 0.5% new ones. But still, I noticed some sensors have offset and/or sensitivity out of manufacturers specification. There are two 1206 resistors on the board with approx 55R and 6k8 value and they are used to tweak offset/sensitivity precisely. Are they normal 1206 resistors just with no marking on top or are they something special (based on their look)?

[Doctorandus_P]

My guess is that those big resistors are laser trimmed. I.e, they first get soldered, and then they use a laser to ablate resistive material (which increases the resistance) until the bridge is in balance. When looking at the horizontal resistor in the full resolution picture, it looks like the surface is slightly rough in the "missing section", and this could be a result of the laser ablation.

[gaminn]

Thanks for the info. I was wondering how the manufacturer achieves declared accuracy. I will just replace the trimmed resistors with ordinary ones with correct value to achieve declared offset and sensitivity ratings.

[gaminn]

Any idea where to get 1206 6k8 resistors with wide resistance variance so I'm able to tweak the offset and sensitivty of my sensors? I need anything between 6k7 and 6k9 with 10 ohms precision. I have 6k8 5% resistors in stock but all of them are 6740 +- 20 ohms, so I never get close to 6k9. I also searched mouser but for my resistance range and 1206 case, they have only 6k73, 6k8, 6k81, 6k9. I might cover the whole range 6k7 - 6k9 if I buy enough pieces of each resistance on mouser, but is there a better solution?