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Looks like a voltage regulator with marking AC or A0, and 9C on perpendicular to the SOT23 element corpus length.

What it might be?

Element

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Anton Miroshnichenko
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    Welcome! Best guess: BJT due to 1 kohm on base. If you probe and trace out what pin 2 and pin 3 goes to, we can perhaps narrow down further. – winny Feb 01 '23 at 08:53
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    It looks nothing like a voltage regulator? I'd say it rather looks like a diode, BJT or MOSFET. – Lundin Feb 01 '23 at 08:53
  • The SO8 might be a voltage regulator however, given the inductor next to it. – Lundin Feb 01 '23 at 08:54
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    Why do you say this looks like a voltage regulator? Is there something on the other side that gives you that idea? Show it, if so. – Hearth Feb 01 '23 at 14:38
  • I updated with new photos – Anton Miroshnichenko Feb 03 '23 at 11:24
  • This site might help https://www.s-manuals.com/smd . There are hits for both A0 & 9C. The PNP transistor look possible https://www.s-manuals.com/pdf/datasheet/b/c/bc856-bc860_fairchild.pdf , but you'd want to map out the schematic. – colintd Feb 03 '23 at 17:31
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    @AntonMiroshnichenko If you see "Q" on the silkscreen, e.g., "Q1", it indicates that it is a transistor. ICs such as voltage regulators would normally use "U" or "IC". – Andrew Morton Feb 03 '23 at 18:06

1 Answers1

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This part AO3400, a MOSFET, has the A0 main marking, and a lot marking just where you can see 9C (p6 in the datesheet).

Trace widths make sense, with thick for D & S, and thin for gate with a 1K gate drive resistor.

Also the datasheet specifically calls it out for "load switch" or in "PWM applications", which is what it looks like we have here, especially as the gate drive is coming from the main IC, and the D & S connections match with where the main supply wires come in.

As it would be the main current carrying element in a converter/regulator, it is a natural component to overheat if the output was shorted or excessive load drawn.

Finally it is an "economy grade" component, which fits with other parts we can identify.

colintd
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