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Akasa AK-P460FG BL (Silverstone ST46F) burnt resistor

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    Akasa AK-P460FG BL (Silverstone ST46F) burnt resistor

    Got my hands on a Akasa AK-P460FG BL (pretty much same device as Silverstone ST46F), which I though would have been an easy recap. After several recapping sessions I couldn't get the PSU to fire up (5VSB comes up, and MB light turns on but the PSU doesn't start up), then I managed to notice one burnt up resistor (R56 I believe) right next to the primary cap. The resistor has burned from the middle (picture 1 in attachments), so only the first and last colors can be seen: they are brown and brown/gold, can't really identify which for the latter. The resistor measured 6.65 kOhm with a multimeter, which doesn't match with the brown stripe so it seems to have partially failed.

    First I though that the burning would have been caused by a failing primary cap. It is a Teapo LXK 270uF 450V, but at least the capacitance turned out to be in spec. It could also have been caused by the smaller caps near to the primary, especially one near to the heatsink (original was leaning to the heatsink), but that cap turned out to be in spec too, at least for the capacitance. I changed that cap to another one just in case, from Jamicon TK 1uF 50V to OST RLG 2.2uF 50V. I haven't yet checked the other smaller cap if it's faulty or not.

    Can you give suggestions on what caused the resistor to burn? There was one failed Teapo SC 470uF 16V, which might have been on the 5VSB line as it was next to a Teapo SC 1000uF 6.3V cap. I would also need to know the value of the failed resistor. I tried searching for pictures of Akasa/Silverstone that would clearly shown the color code, but coudn't find any good ones. The closest one I found is attached as the last picture. I would GUESS that the second stripe is green.

    Thanks in advance!
    Attached Files

    #2
    Re: Akasa AK-P460FG BL (Silverstone ST46F) burnt resistor

    I just tried replacing the burn resistor with a 1.8k Ohm resistor (also replaced the primary cap with a 220uF 450V, to rule out a bad primary), but no change in behavior; motherboard led turns on, but nothing more happens. One noticeable characteristic is that when the power is switched off from the main switch, the voltage in the circuitry dies out faster than usual, and produces a clearly audible "zzip" at the moment when the led turns off.

    My next move would be to try a ~15 kOhm resistor. Any other suggestions would be warmly welcomed, as some other components might have gone bad too.

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      #3
      Re: Akasa AK-P460FG BL (Silverstone ST46F) burnt resistor

      The resistor could be a low ohm value one.

      Most likely, the 5v standby circuit has gone pop. Check the transistor on that little heatsink near the smaller transformer.
      Muh-soggy-knee

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