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I am trying to fix a controller that manages a string of lights. The input and output voltages are 24 V. The output voltage seems to vary slightly in order for the lights to change colors based on the voltage applied. There are the outputs and one of the outputs isn't working like the others. As I poked around I came across two components that seem to be shorted because of the way it behaves is different from other similar components on the board. So I'm taking a chance and want to replace it, but I can't figure out the part number. Here is a picture on the post of the surface mount component I want to replace. It has the numbers 3401 on top and it may include a 'T'. Does anyone know if the part number is 3401 and if this component matches what I'm looking for: https://www.digikey.com/en/products/detail/goford-semiconductor/3401/13664831 enter image description here

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  • \$\begingroup\$ Looks SOT-23. Can you trace out the schematic around then? \$\endgroup\$
    – winny
    Commented Dec 9, 2022 at 23:49
  • \$\begingroup\$ Unfortunately, I do not have a schematic for it. However, here is some more information about the device: fccid.io/2APJZ-TW200117 and here are more internal pictures of the item in question: fccid.io/2APJZ-TW200117/Internal-Photos/Internal-Photos-4655738 \$\endgroup\$ Commented Dec 10, 2022 at 0:23
  • \$\begingroup\$ I understand that, but if you follow the tracks, you can draw one from how things are connected to them. Also, with a multimeter, can you check if pin 2 of the left guy is grounded? \$\endgroup\$
    – winny
    Commented Dec 10, 2022 at 9:02
  • \$\begingroup\$ Both bottom legs are connected to ground. It seems like the component is shorted for sure. I'm hoping you're correct on the part number. I really want to replace the component and get this working. Do you know where i could buy it? \$\endgroup\$ Commented Dec 13, 2022 at 0:24

2 Answers 2

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Definitely looks like a transistor. Could be Cystech MTP3401N3? Doesn't match the 'T' though.

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    \$\begingroup\$ Looks promising. I'm not sure what's up with the T. Another thing to note is that there is a 220ohms resistor connected to the left pin of the transistor from the bottom. \$\endgroup\$ Commented Dec 10, 2022 at 0:33
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Best guess: MMBT3401 NPN transistor. Common as dirt.

Datasheet: https://www.onsemi.com/pdf/datasheet/mmbt4401lt1-d.pdf

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  • \$\begingroup\$ 3401 or 4401? All I've seen are alphanumeric coded. \$\endgroup\$ Commented Dec 9, 2022 at 23:57

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