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I am trying to fix a RS485 circuit. There is 3-pin protection components on both A and B pins. The component is connected serially to the line and mid pin is grounded. There is no label on the component.

The resistance is nearly 0 ohm and the component is short circuit by defult.

Could you please help to identify this component?

Protection Component Schematic

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  • \$\begingroup\$ Short circuit between which pins? \$\endgroup\$ – winny Jul 9 '19 at 12:09
  • \$\begingroup\$ the resistance between the firs and third pin is 0.5 ohm. mid pin is grounded. I heated the component to 300 Celcius but the resistance didnt change. \$\endgroup\$ – Mustafa Aygün Jul 9 '19 at 12:12
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It quite likely is one of the NFE series of Murata.
Looking at the size, I guess NFE61PT 2706(6816).
The chip "EMIFIL" NFE61PT is a T-type circuit EMI suppression filter.

Bad quality image from the datasheet reveals the low DC resistance you're measuring between input and output. Therefore, I think it's quite likely the component is not broken.

enter image description here

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  • \$\begingroup\$ Yes this is a EMI suppression filter. But as there are no markings on the device it is impossible to know which exact device it is. \$\endgroup\$ – Justme Jul 9 '19 at 12:33
  • \$\begingroup\$ @Justme True. The same applies to SMD resistors. You never know exactly what component has been used. Therefore I wrote: it quite likely is one of the NFE series. OP should confirm the components dimension with the datasheet's dimensions and could further desolder it and measure the insertion loss using a spectrum analyzer. \$\endgroup\$ – Huisman Jul 9 '19 at 12:52
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    \$\begingroup\$ But as I just edited: the component is likely not broken, so probably an exact part number isn't required as there is no need to replace the component. \$\endgroup\$ – Huisman Jul 9 '19 at 12:52
  • \$\begingroup\$ Indeed, based measurements that component is not the problem. \$\endgroup\$ – Justme Jul 9 '19 at 12:56
  • \$\begingroup\$ @Huisman, thanks for your help. The component is exactly Murata NFE. The part number isn't important because the component is working. \$\endgroup\$ – Mustafa Aygün Jul 9 '19 at 16:01

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