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  • I need electronics help!

    I have a Samsung Plasma TV that was given to me. It had sound but no picture. Pulled it apart and found a burnt up MOSFET (transistor). They had a power spike at the home and I'm guessing this chip took the brunt of it for some reason. I found a similar model numbered chip on e-bay but was wonder if it truly is the same. Any ideas?

    The offending chip is again a MOSFET (transistor) part #
    B20NK50Z
    GK120 VW
    CHN 739

    My question is can I use this MOSFET to replace it. Honestly, if it works great, if not, I really dont care as it was free.

    STB20NK50Z Manu St Encapsulation to 263 N Channel 500V 0 23 Ohm 17A | eBay

    Thanks!

  • #2
    Re: I need electronics help!

    Their are a few cross reference lists free online that will give you a match. Did you test it? They are sometimes discolored by heat but still fully functional.

    A more common failure is in the bank of charging capacitors.

    Electronics is more involved than just replacing the offending component. What should be looked into is what supporting component(s) likely failed, causing the failure.

    If your going to do it yourself be careful you don't get "poked" and use a low heat soldering iron rather than a soldering gun (magnetic field can blow out sensitive components)

    Might want to ask a local repair shop for a quote (might be cheaper than you think)
    Personally, I would trust Galco or a similar electronics place before E-bay.

    Good luck

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    • #3
      Re: I need electronics help!

      Try Mouser, Newark, or DigiKey.

      But as John said, there will more likely be other components besides this one that are failed or will fail in the near future. Without the proper diagnostic equipment you won't be able to take measurements at various test points and will be chasing these failures for a long time.

      What do you know about ESD and do you have the proper tools and training to deal with it?

      Best bet is take it to a repair shop or use it for target practice.

      Oh, and note that Mouser has this part flagged as obsolete, at least from one manufacturer, so your sources may be limited to what stock various places have on hand.
      Last edited by Bob D.; 01-26-2013, 07:22 AM.
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      Comment


      • #4
        Re: I need electronics help!

        Thanks guys. I figured since these chips are only a few bucks I'd at least give it a shot. The chip that failed actually just about burned through the PCB it got so hot. From what I read, they are a switching transistor. And this one actually delaminated and you can see where it appears to have hung closed and welded one side of the gate. There is no evidence of failing capacitors anywhere. (The typical bulging or leaking) and no other discolored parts that I've usually seen. I've been lucky before replacing resistors, capacitors and other failed components with good results. Figured why not. There is a local TV parts outfit that does have this board available for 120 bucks... not sure what route to take yet.

        Comment


        • #5
          Re: I need electronics help!

          I completely agree with John and Bob. Personally I don't do board level component repairs, except the simplest of things. I grew up with "tubes" so when it comes to integrated circuits, I have some challenge in "wrapping my head around that" (read that as no confidence). Probably, becaues as they said... one component failure usually effects others; especially when it comes to power surges. (The conductive link between components, and their proximity, is so minute that a component failure is usually easily bridged by the high current of the surge.)

          However, given your stated experience, what have you got to loose. My biggest concern would normally be that someone might introduce too much heat in the soldering or worse... static discharge that would cause other components to fail... and thus a much wider problem because of your attempts. If however, you've done similar component work and you know how to properly remove and replace a soldered component then you may be okay.... just protect the circuit by ensuring you take proper static discharge (ESD) precautions.

          Regarding the component itself, I think I'd take the previously posted advise and check to make sure that the replacement is properly valued. There are tables on the web, but I would check with a local tech or call one of the places that referenced to make sure.

          CWS

          Comment


          • #6
            Re: I need electronics help!

            Your best bet is to try and identify the manufacturer of the original transistor and then look up their datasheet (usually these can be found online) and then look for a part with a similar spec. it is likely the one you found is functionally identical but a lot of times they are not exactly the same if you look at all the parameters in the datasheet.

            Judging by what you posted on the replacement part it looks like it would have been part of a power supply. Something of that rating is unlikely to be used anywhere else. My guess is that there are other things possibly wrong with it but if you don't mind having a go you can try replacing it and seeing what happens.

            MOSFETs are commonly used as switches but I've also seen them used in linear circuits such as amplifiers. MOSFET just refers to the fact that it is based on FET technology so the input voltage develops an output current (unlike A BJT which is a current controlled current generator) but depending on the manufacturing parameters they can be used in linear circuits.

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            • #7
              Re: I need electronics help!

              Thanks Bob and others. I ordered a new chip from Mouser today and its the same manufacturer as well. Also ordered a bunch of capacitors to repair two failed power supply boards from two Samsung 19" monitors I have in pieces on my desk, so thank you very much for that reference! Going to possibly pick up 2-3 more TVs next week to tinker with. Might even apply for an opening at a local TV parts/salvage place for a technician. Just want part time for experience and some extra cash. I miss fixing this sorta stuff.

              Comment


              • #8
                Re: I need electronics help!

                Unfortunately fixing at component level will become a thing of the past if it has not done so already. Most of the functionality of modern electronics is integrated within chips so there is not much you can do in terms of replacing individual transistors etc. The only things that will remain discretes are things like large caps, power transistors etc. Analog filters are now commonly replaced by digital filters and so inductors and caps are replaced by multipliers and adders. All this can be done inside a chip with digital logic.

                Replacing chips with BGA style packing with thousands of pins is not a DIY job. I personally almost never open up any electronics these days with a view to fixing – just not worth my time. Only exceptions are straightforward things like swapping out hard drives.

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