Confusion about BJT identification

Semiconductor Discrete Semiconductor Products
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1

I need to replace two SOT-23 transistors that have markings “2F” and t2X" which I have identified as PMBT2907 and PMBT4401, respectively. These are both BJTs (PNP and NPN, respectively). However, when testing with a DMM they appear to be more like JFETs. That is, the diode drop across pins 3 and 1 is the same as pins 3 and 2, suggesting that pin 3 is the base. But the base of a SOT-23 BJT is pin 1, whereas the gate of a SOT-23 JFET is pin 3 which agrees with my readings. This occurs with both PNP and NPN devices. Am I missing something here? Is it possible that BJT and JFET devices could have the same markings?

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Hello @jfgerling,

Possible, but unlikely as the root 2907 implies a PNP 2N2097 heritage and the root 4401 implies a NPN 2N4401 heritage.

Here is the pinout for the Nexperia PMBT4401,215

Pinout for the Nexperia PMBT4401,215
Pinout for the Nexperia PMBT4401,215680×209 17.1 KB

Possible explanations:

  1. Remove from circuit before performing the classic “diode-as-transistor” test.

  2. Meter may not drive the diode hard enough - digital vs analog meter.

  3. Bad device.

Recommend you verify the method using a spare 2N2222 or 2N3904 or whatever other NPN is available in your shop.

Best Wishes,

APDahlen

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Thanks, APDahlen. I was testing in-circuit, so will remove the devices and repeat. I’ve ordered replacement BJTs on faith they are correct.

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