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Thread: SMD id

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    Default SMD id

    Ok so you're working on a TV and find 2 SMD components that are burnt, a transistor and a zener diode, You can't read any markings and there's no available schematic for it.
    What do you do ?



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    You're gonna call, Ghostbusters?

    Phone a friend?

    Or you give us TV model, or Board number , location identifier.

    Is this the LG EAY62512701 PSU ? or what?
    Last edited by tw2005; 16-07-17 at 02:30 AM.

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    Quote Originally Posted by tw2005 View Post
    You're gonna call, Ghostbusters?

    Phone a friend?

    Or you give us TV model, or Board number , location identifier.

    Is this the LG EAY62512701 PSU ? or what?
    No, not the LG.
    The question was really asking about the thought process, what do you do?, how others handle the problem?

    This one's a Changhong 65" UD65D2800 power supply.
    47u 450v and 12u 450v caps swollen.
    FET Q4 fizzed, big hole in it.
    Fuse F1 blown.

    SMD's in question are Q1 and ZD2 (adjacent to Q4).
    Mr google didn't help at all.

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    Hmmm, I see. well I don't really. Pity, I found a full schematic for the LG

    Well, I'd say you've tried the obvious searching the board number and looking for images. That's what I'd do or see if that board is fitted to ther models in other markets?

    Not exactly mainstream, tough egg to crack.

    Can't hurt putting some clear images up. Also I find imgur pretty good for that.

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    is there another FET the same as Q4 on the board?

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    well loopyloo you have a bit of a dilemma on your hands.
    I would try and trace out the circuit to find out what q1 and zd2 are actually doing.
    they could be driver for q4 or some sort of protection circuit.
    switch mode power supplies are easy to trace the circuit and draw it on a piece of paper.
    from there you could look for similar circuits to see if other circuits use similar components.
    Sounds like the chopper q4 fried up and took those components with it and probably others as well but they might not be as obvious.
    The other option is to find out what output rails the power supply is delivering and try and find a substitute.

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    sometimes a board uses multiple components of the same type - you could try and find a similar component and test it out of circuit to determine what it is

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    Quote Originally Posted by tw2005 View Post
    is there another FET the same as Q4 on the board?
    Unfortunately no Q4 is unique.
    Forgot to mention R33 (0.1ohm) resistor has burnt open.

    Suspected cause of the fault is small cockroaches. There were about a dozen inside the TV and a couple of charred ones sitting on the legs of Q4.

















    Last edited by loopyloo; 16-07-17 at 12:32 PM.

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    Found nothing except a bunch of overseas models with the same board. Also a shame the underside has a black sheet otherwise the Shopjimmy image may have helped.

    50326502000060, HKL-650201, HKL-650401, 401-2Q401-D4202

    Hitachi
    LE65K6R9, 65K3, 65L6

    Haier

    LE65B7000TU

    Sansui
    SLED6516

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    As Q4 is on the primary side it'd be a fairly safe bet that it's an N channel mosfet rated at least for 600V, 6A or greater.
    Seems odd for all those components to fail together unless there was a high voltage spike or the bridge rectifier short-circuited applying mains AC voltage across the caps & mosfet.

    The caps might have been swollen prior to the fault - check the ESR
    and those SMD PWM controller chips are likely to be traumatized as well
    Last edited by Skepticist; 17-07-17 at 11:13 AM.

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    Quote Originally Posted by Skepticist View Post
    As Q4 is on the primary side it'd be a fairly safe bet that it's an N channel mosfet rated at least for 600V, 6A or greater.
    Seems odd for all those components to fail together unless there was a high voltage spike or the bridge rectifier short-circuited applying mains AC voltage across the caps & mosfet.

    The caps might have been swollen prior to the fault - check the ESR
    and those SMD PWM controller chips are likely to be traumatized as well
    It's a 24N60M2 ... N-channel 600v 18A.
    I thought it might be the 2 fried cockroaches on the FET pins.
    Both caps are at 9.9ohms.
    Bridge rec is ok.

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    So it sounds like the caps had been drying out for a long time until the supply on load was running with a pretty much unsmoothed full-wave rectified supply. I'd say the roaches were either collateral damage or the straw that broke the camel's back but the good news is HV spike is looking unlikely so components not in the direct path of the fault current should be still in good condition.

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    For a small fee this company will fix any switch mode power supply

    they are very good - just send them the supply - nothing they cant fix

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    Quote Originally Posted by Tiberius View Post
    For a small fee this company will fix any switch mode power supply

    they are very good - just send them the supply - nothing they cant fix
    Small fee ???
    Have you sent them PS's ?

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    Yes - they are reasonable - you normally pay less than the supply is worth

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    Any joy or new revelations with this supply?

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    Quote Originally Posted by Skepticist View Post
    Any joy or new revelations with this supply?
    I put it aside for a while to work on the LG.
    Got a few more to look at too. You might hear about them yet Lol

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    One of the main caps is a 120uF at 450v. Can I use a 100uF in its place in this circuit ? 120uF is really expensive.

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    That's the main capacitor in the power supply and 100uF will be fine - they generally have about a 20% tolerance anyway.

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    Ok good.
    Would you like to hazard what U4 might be ? Not sure if it's faulty.
    I think I worked out what the components are bar one but now I can't find that list. Have to do it again.
    I'm going to attempt to sketch out some of the circuit, not one of my strong points.
    Last edited by loopyloo; 25-08-17 at 07:20 PM.

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