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Trying to debug a broken circuit board and the component circled in red seems to be key to understanding the behavior. I've scoured the internet as best I could, but cannot find any reference to anything even starting with EJenter image description here

I searched: https://www.sphere.bc.ca/download/smd-codebook.pdf

https://www.digikey.jp/en/pdf/m/micro-commercial-co/mcc-smd-marking-codes

https://alltransistors.com/smd-search.php?search=EJV

Any tips for where to look next?

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  • \$\begingroup\$ Some chips have proprietary markings that aren't listed. If the catalogs fail, try figuring out what it's connected to. If you're lucky you might be able to figure out what it is that way. You might be able to find out by contacting the manufacturer of the original device(board) if they're repair friendly. If an otherwise common part is obfuscated this way, it could be they don't welcome outside service, but it doesn't hurt to ask \$\endgroup\$
    – K H
    Jan 29, 2021 at 8:48
  • \$\begingroup\$ You should provide more information about why you believe that particular component is suspect. It's marked Q and it's surface mount so there's a good chance it's a mosfet or switch. As for current and voltage ratings, you have to figure out a good portion of the circuit to guess at that. \$\endgroup\$
    – K H
    Jan 29, 2021 at 8:51
  • \$\begingroup\$ I also suspect it to be a transistor. While on, I measure 6V at one pin and 3.3V at another, and 0 V on the last. The 3.3V pin is connected to a 3.3V rail elsewhere on the board, and the 0V is not connected to ground. The reason I think this is an important piece is that the 0V pin is connected to the voltage supply of this motor controller (shown top left of photo). I'd expect this to be 1.8V to 3V according to the datasheet, not zero. I currently suspect this is EJV transistor is open to protect the motor control pin at max 3V. \$\endgroup\$
    – topher217
    Jan 29, 2021 at 9:00
  • \$\begingroup\$ Do these SOT-23 have standard pin assignments? I.e. is the gate always in the same place or does this vary by manufacturer? I can search through a bunch of different datasheets, to test a few sample points, but wondered if anyone knew if this is standardized or not. This could help eliminate some guessing and make my theory of what is going on a bit more robust. \$\endgroup\$
    – topher217
    Jan 29, 2021 at 9:02
  • \$\begingroup\$ Don't answer in the comments. Hit edit at the bottom of your question and use that information to nicen it up a bit. To get help with repair and troubleshooting on here, you both have to show a base level of skill, and if possible do your own grunt work. One potential reason to special order a weird version of a standard part is to get the pinout you want, so theoretically they could be nonstandard pinouts. I'm not actually sure what standards exist, but similar parts in similar packages I've used have had the same pinout. \$\endgroup\$
    – K H
    Jan 29, 2021 at 9:08

1 Answer 1

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The best option I can find would be the Nexperia PMV33UPE, a P-Channel Power MOSFET with marking EJ%.

The % in the marking is a placeholder for a manufacturing code, which I cannot find any further details on. It could conceivably be multiple characters, perhaps including date code information.

The pin-out seems to make sense, in both cases the gate is connected to the skinny trace in your image, and the source/drain are connected to fat traces. In the case of the lower right, the source connectes to C68 and a possible power plane. The drain connects to an inductor, along with the cathode of a diode (whose anode is GND). This would be the classic topology of a Buck converter, so would make sense for a PMOS with this pinout to be used.

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  • \$\begingroup\$ Awesome find! Yes, you inferred most of what I had plus more! There are also a fair amount of other Nexperia components on the board if that adds any higher probability. I'll mark as correct until I find something that would contradict your claim. \$\endgroup\$
    – topher217
    Jan 29, 2021 at 9:12
  • \$\begingroup\$ @Tom_Carpenter, could you teach a man to fish please? :D Would you mind adding a bit to your answer as to HOW you found this? Hoping to add your search tools to my arsenal next time I have to search. \$\endgroup\$
    – topher217
    Jan 30, 2021 at 8:18
  • \$\begingroup\$ @topher217 A lot of Googling, that's really all there is. I just try different combinations of package name, and bits of the text from the IC, and some keywords such as "package", "IC", "SMD", "marking". \$\endgroup\$ Jan 30, 2021 at 10:21
  • \$\begingroup\$ Well hats off to your Googling skills then. Thanks again! \$\endgroup\$
    – topher217
    Jan 30, 2021 at 10:21
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    \$\begingroup\$ @topher217 This was the search history until I found the linked part. There was a lot more of the same after that trying to find others. \$\endgroup\$ Jan 30, 2021 at 10:25

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