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find faulty compnent on ATX power supply

pharaon

Oct 28, 2014
444
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Oct 28, 2014
Messages
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it's ATX power supply i'm working on
the issue is in 5V output, it drop to 3V when i connect it to 12V pc fan, and the fan keep kicking without spin
i hear fry sound from this side of main transformer but can't detect exactly which component making the sound or responsible for not delivering enough current to 5V line output
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Bluejets

Oct 5, 2014
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Oct 5, 2014
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Last edited:

pharaon

Oct 28, 2014
444
Joined
Oct 28, 2014
Messages
444
in the below image to the right is the connector of cooling fan, it doesn't start and voltage at connectors drop from 12 to 3 when the fan is connected, i back traced it and removed smd NPN transistor that is shorted and this is it's datasheet
http://elektrikaetoprosto.ru/ebc849c.html
i replaced it with STC945 NPN transistor since i couldn't find smd one but the same issue still exist.
also ther's those two gray and yellow wires connected to the heat sink beside cooling fan tracks .
what could be the reason for this issue

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