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    tv smps need help for identifying smd components

    Hello, would like to ask you fir some help. I am working (for some time now) on SMPS from LG plasma TV. I have found
    bad smd transistors (or diodes?) and capacitor without any markings on it. Could someone take a look? Any help would be appreciated! ;]

    Click image for larger version. 

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    Last edited by seldon; 13th September 2017 at 07:12.

    •   Alt13th September 2017, 06:59

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    Re: tv smps need help for identifying smd

    Hi,

    Yes, I took a look on your picture.

    What exactely is your question?

    Klaus



    •   Alt13th September 2017, 07:42

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    Re: tv smps need help for identifying smd

    In my photo I marked (with blue squares) two smd transistors (i hope it's a transistor) which are open and smd cap near dridge rectifier which is in question (reads shorted in circuit), they don't have any codes or markings (to identify) on them. So my question is could you suggest me alternative parts for these components to replace. I couldn't locate any schematics of these smps.
    Last edited by seldon; 13th September 2017 at 08:20.



    •   Alt13th September 2017, 08:12

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    Re: tv smps need help for identifying smd

    Hi,

    * impossible to see any part details in your photo.
    * I doubt you can verify the function of the devices "in circuit"
    * without detailed type / name of the tv, nobody can look for a schematic.

    Hopefully the designer of this board sees your thread and can help you.

    Klaus



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    Re: tv smps need help for identifying smd

    I know everything about TV :)

    LG plasma 42PXRVB ZA and this SMPS is SANKEN PSC10089G M hope that helps.

    All parts metiond where pulled out of circuit and tested as it is.
    Last edited by seldon; 13th September 2017 at 10:00.



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    Re: tv smps need help for identifying smd

    Is it even possible to find commecrial TV's smps scehmatics? It seems that manufacturers keep it in secret.



    •   Alt13th September 2017, 11:55

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  7. #7
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    Re: tv smps need help for identifying smd

    Hello seldon,
    To confirm that the cap in question is actually short circuited, you need to remove and
    measure it out of circuit.
    Once its out and you find it ok, then the short is elsewhere. But more than likely one
    of your semiconductors is the real culprit. Caps rarely go SC. Also, most non-polarized
    SMD caps are tan in color, compared to resistors being black. Its a tad hard to see the
    cap/resistor in question. You need to provide a more focused picture.
    SMD caps won't have any marking on them at all. But the common values on them are
    usually 0.1uF or 0.01uF.
    You need to measure (with an ohm-meter) across the point where the cap/resistor was
    sitting. If there still is a short then you need to trace that track back and isolate anything
    associated with the rail that's shorted, but not the ground rail. But use the ground rail
    as your reference to measure the shorted rail.
    By the way, has the main fuse blown? If so, how violent was it? If its a non-glass type,
    then the last question is moot.
    If the SMD transistors have a circuit designation of Q or Tr, then they will more than likely
    be transistors or FET's. But unless there are actual identifying marks on the transistor bodies,
    it would be near impossible to determine their type without a schematic diagram.
    As I strain my eyes to see any circuit designations, the transistors in question are marked
    with "Q".
    Since these transistors are mainly the switching types, you could replace them with standard
    SMD transistors, such as: BC846 (NPN) or BC857 (PNP).
    Your only problem is in determining what types yours are i.e. NPN and/or PNP's. You need to
    also determine the pin-outs of each i.e. B, C and E.
    You really need to remove the transistors to determine 100% that they are shorted. But measuring
    them in-circuit should be done with an ohm-meter, and not the diode check. If it just reads low ohms
    and not a dead short, then more than likely those transistors are serviceable.
    Is there any way you can get a more closer picture taken of the solder side of the PCB?
    Also would be good to get a picture of the component side as well.
    Regards,
    Relayer



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