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I'm currently trying to repair a board and I found this SOT23 component marked as X3,but i not found this ic Model number. At first I suspected that the chip was an npn transistor, but this transistor's base is pin 3 in sot23-3. However, the triode base that can be found at present is all in pin 1. So I don't know what type of chip this is.

The junction voltage between pin3 and pin1 、pin2 is 0.7V, and the impedance between pin1 and pin2 is about 120 Ohm. These characteristics are not quite consistent with the characteristics of mos tubes. Moreover, the chip should be analyzed from the circuit because of current amplification, rather than voltage amplification enter image description here enter image description here

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  • \$\begingroup\$ Could you trace out where each pin goes and what it connects to? \$\endgroup\$ Sep 13, 2023 at 8:47
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    \$\begingroup\$ Could be a 2SK94 JFET, which has the same X 3 marking. \$\endgroup\$ Sep 13, 2023 at 8:49
  • \$\begingroup\$ These solder holes lol very bad. The flux residue looks much darker than usual. Are you perhaps using plumber's solder material instead of electronics solder and flux? \$\endgroup\$ Sep 13, 2023 at 8:54
  • \$\begingroup\$ marszhang - Hi, I see that twice you have posted something in the box below, labeled "Your Answer", but they were not answers. Stack Exchange rules differ from typical forums. If you want to add more info to your question, please edit the question. Since you asked the question, the only time you would use the box below labeled "Your Answer" is if you have answered your own question, so it can be considered closed i.e. you are posting the full & final answer (which should be different to any other answer - don't just repeat another answer). Ask on Electrical Engineering Meta with any questions on the rules. \$\endgroup\$
    – SamGibson
    Sep 14, 2023 at 1:45
  • \$\begingroup\$ marszhang - Hi, You said: "These characteristics are not quite consistent with the characteristics of mos tubes." Is "tubes" an accidental mistranslation of "transistor" or "FET"? Please can you review and correct, if necessary? Use of the word "tubes" may confuse readers. Thanks. \$\endgroup\$
    – SamGibson
    Sep 14, 2023 at 1:51

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The 2SK94 JFET looks a plausible match. From the little of the PCB that is visible, it also seems a good match with the surrounding components.

It's produced by various manufactures, but here's a link to some on sale from eric1688.com enter image description here.

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