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Thread: blown RT1

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    Senior Member omega99's Avatar
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    Default blown RT1

    have a component on a pcb that is cactus, has RT1 next to it and a symbol of what looks like a resistor under it. looks like a brown fat ceramic capacitor - anybody know what this component might be?
    its inline on the 240v active incoming side
    resistor are marked R3 etc and varistors are VAR2 etc
    woteva



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    Sounds like a thermistor which would be NTC (negative temperature coefficient) to limit the inrush current at switch-on.

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    sounds like a thermal resistor to me ????

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    nothing written on it and it is open circuit, now to guest what size thermistor.
    its connected to a 400v 4.7uF cap
    woteva

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    Something like this one might go close to doing the job depending on what the typical operating current of the device is:


    Trace out the circuit first to be more certain of what you really require though. Usually the thermistor is just to tame the initial inrush current charging the capacitors on the mains side of the power supply at switch-on so there could be some other major failure to overload it to the point of destruction. IE it's likely to be just a symptom of the real problem that's further downstream and that needs to be found and fixed so you don't go sacrificing replacements as well.

    Oh: And DON'T go probing the circuit with live mains attached.
    Last edited by Skepticist; 18-12-19 at 09:49 PM.

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    Quote Originally Posted by Skepticist View Post
    Something like this one might go close to doing the job depending on what the typical operating current of the device is:


    Trace out the circuit first to be more certain of what you really require though. Usually the thermistor is just to tame the initial inrush current charging the capacitors on the mains side of the power supply at switch-on so there could be some other major failure to overload it to the point of destruction. IE it's likely to be just a symptom of the real problem that's further downstream and that needs to be found and fixed so you don't go sacrificing replacements as well.

    Oh: And DON'T go probing the circuit with live mains attached.
    ok no probs
    woteva

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    omega,

    Post a picture. It's a lot easier for people to help

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    too late already let the smoke out, seems a component upstream might have been the cause.
    woteva

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    Sounds like an inrush current limiter. Any idea what shape it was ? Will help.
    You can short it out and apply power through a Variac or use a 60W light globe in series with the Active.
    Then fault find.

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