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    Why this transistor,fuse and diode burned when i turn on the power supply,what cause_

    Please i need your help, if anyone can help me.
    I have this power suppply " Lambda Alpha 600W power supply " ,
    When i turn on the power supply the transistor in the picture (STP7NB60 ) burned ,
    and the fuse blow .
    (original transistor is IRFIB7N50 is replaced by STP7NB60 )

    i have checked for short circuit but i dident find any shorted element, i have checed all diodes and capacitors,fet transistors in
    the board,they are good.

    when i i turn on the power supply without this transistor(STP7NB60) the fuse is ok(not blow) and the voltage in the
    rectifier diode is good, when i just put the transistor(STP7NB60) in the board the fuse blow and this transistor burned in MOMENT .

    why this happened, what cause it?. how to fix it please..

    The images


    I need your help please..
    THANK YOU VERY MUCH FOR READING.
    Last edited by interneti; 13th February 2012 at 15:08.

    •   Alt13th February 2012, 11:42

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  2. #2
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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what ca

    Quote Originally Posted by interneti View Post
    Please i need your help, if anyone can help me.
    I have this power suppply " Lambda Alpha 600W power supply " ,
    When i turn on the power supply the transistor in the picture (STP7NB60 ) burned ,
    and the fuse blow .
    (original transistor is IRFIB7N50 is replaced by STP7NB60 )

    i have checked for short circuit but i dident find any shorted element, i have checed all diodes and capacitors,fet transistors in
    the board,they are good.

    when i i turn on the power supply without this transistor(STP7NB60) the fuse is ok(not blow) and the voltage in the
    rectifier diode is good, when i just put the transistor(STP7NB60) in the board the fuse blow and this transistor burned in MOMENT .

    why this happened, what cause it?. how to fix it please..

    The images


    I need your help please..
    THANK YOU VERY MUCH FOR READING.
    check the fet you are replacing with whether it is p-channel or n-channel,if the first one is n-channel which i think and the other is p-channel then you must have to change its drain and source connection,if this not ,check what is the voltage on gate with respect to negative.the voltage on gate should be like 15v.regards



  3. #3
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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what co

    IRFIB7N50A pdf, IRFIB7N50A description, IRFIB7N50A datasheets, IRFIB7N50A view ::: ALLDATASHEET ::: link for IRF1B7N50A
    http://www.datasheetcatalog.org/data...onics/5325.pdf link for STP7NB60 .
    can you see in those link if this replacements is good . I have checked other complenets and they are good,
    some resistor near trnaistor(STPNB60) was burned, i replaced them with new..so all components looks good.
    Why this transistor burned imediately when i turn on the power supply ??...



    •   Alt13th February 2012, 23:56

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  4. #4
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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what co

    Need more info, what’s the hole history about this power supply? Have you changed also other components?
    Next time try a better PCB solder side photos.



    •   Alt14th February 2012, 01:25

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  5. #5
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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what co

    when i dissasemble this power supply at first time , i found there the transistor IRFIB7N50 shorted ,a diode and another transistor near it
    was shorted to ,i replaced the transistor IRF... by STP7NB60. and other component with their equivalent, near
    Transistor IRFB7n50 i found some smd resistor burned(open resistors ). i dident replace them at first time.because
    i dident identify any shorted elements. then i turn on the power supply and in moment the fuse blow up,and the
    new transistor STP7NB60 was burned(shorted), and a diode near it goinig in shorted/ i check again for any
    components in shorted that cause the fuse burned.but again i dident identify any shorted circuit,
    i check all diodes, all capacitors in board for any bad elements, but they are good.
    I replace this transistor again with STP7NB60 and again when i turn on the power ,the transistor
    burned /

    mister_rf in the picture it is not seriously,it is rubber near that coil,i want to thank you ALL..



  6. #6
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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what co

    if you make a cable up that has a 100W lamp {not low energy types } a filament type

    in series with the live to the psu from mains like

    Neutral ----------------------neutral to psu

    live------\/\/\/\lamp\/\/\/\----live to psu

    earth------------------------earth {if used}

    then your new device wont blow up

    what will happen is the lamp will limit the current to the psu
    if there is a problem then the lamp will light up
    taking up the current that would kill the psu
    when its working ok then the lamp will be dull

    you may find that the bridge rectifier is leaky across some of its diodes

    i use 20mohm range and test in reverse all diodes for any leak...

    hope this help you to stop blowing up your devices you replaced after all they are not so cheep

    i would take the fet;s out and the diode out then power up and test the voltages around the board
    perhaps the fet and i think it will be its damper diode are blowing
    three reason why bad drive bad timing of drive or bad output coils

    i think as the damper diode also goes it will be bad timing

    i would check every single component
    start with the ones that drive the bad devices
    Last edited by picc; 15th February 2012 at 05:20.


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  7. #7
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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what co

    Ok listen interneti
    tell me something : the back of the original mosfet is made from plastic ? And the new on is metal ??? I'm i Right ??
    if yes lets do some tests :

    1 - first use a 100watt light bulb connected in series with the live line. The best place to put the light bulb is the fuse holder area. Remove one of the fuse lead and connect the light bulb across it
    2 - put the new mosfet without sticking the back with the heat sink
    3 - Power it on and begin to observe the bulb.If it brightly lit and stay that way then there is still problem in the power supply. However, if the bulb doesn’t light at all then this is a good sign that the power supply may be working.Use a multimeter to place at the secondary side with power on. If you get some accurate voltage reading from the outputs and the bulb doesn’t light at all, then this confirmed that the power supply is working



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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what co

    I want to thank you all for your helps.
    For moment i cant repair this power supply.

    Again i thank you very much !...



  9. #9
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    Re: Why this transistor,fuse and diode burned when i turn on the power supply,what co

    Anyway .. Try what I Told you and you'll solve the problem :)



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