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    #1

    P-Channel MOSFET testing

    I'm currently having a bit of trouble with a Samsung LCD TV (original thread).
    Plainbill brought me away from thinking it's a faulty mainboard, so i started checking the PSU board, which i assumed was fine after a recap.

    Turns out it probably isn't. Without the PS-ON line connected to anything (mainboard unplugged completely), all output voltages are constantly present (i.e. not just 5Vsb as i thought).
    Tried following the PS-ON line and it lead through a bunch of resistors and a tiny SMD transistor to one of the optocouplers, and also off another way to another blob of resistors, a tiny SMD transistor and a MOSFET, which is labelled "40P03-20", which according to Alldatasheet is apparently a 40P03 P-Channel power MOSFET.

    You can see it in this photo at the top (half cut off)
    I'm gonna take a better pic of that area soon.

    When i went to test it in circuit (diode test mode on my DMM) it showed shorted on all possible pin combinations.
    I got it desoldered today and after heating the solder for a few seconds, it started to smell funny (as if it got awfully hot at one point.. the fried electronics smell).

    Tried checking it according to the simple method posted here
    In this datasheet, there's a block diagram showing a diode between drain and source, so i expected to get a reading one way but not the other.
    Unless I'm too dumb to measure this, it looks like there's a short between drain and source, as no matter which way around I connect the leads of my DMM, I always get 0.00 ohm.

    Am I measuring this wrong or is it simply bad..
    I'm pretty clueless at the moment..

    Someone enlighten me please
    Tags: None
    #2
    Re: P-Channel MOSFET testing

    thats a bad mosfet,
    you can read conformation in this link
    https://www.badcaps.net/forum/showpo...0&postcount=13
    just scroll down to mosfet
    the testing you put up is for a mosfet that is working (but not functioning propely)
    yours has a short, its not working
    Last edited by trebo; 12-12-2011, 09:12 AM.

    Comment

      #3
      Re: P-Channel MOSFET testing

      It is a scary day when one of my testing procedures is used to enlighten someone.

      Long time members will recall I didn't even know what a short, mosfet, and multimeter was back in April 2010.
      Last edited by retiredcaps; 12-12-2011, 04:01 PM.
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        #4
        Re: P-Channel MOSFET testing

        ^lol
        And thanks

        Now I just need to find a suitable replacement.. all I've found so far were TO220, not TO252.. (or I'd have to order 1k of them..)

        edit: this kinda got me thinking if I could use a relay instead of that P-channel MOSFET.. (like other Samsung LCD TVs do)
        The PS-ON signal is 3.xV and from the looks of it, it switches one of two 13V rails
        Last edited by Scenic; 12-13-2011, 04:47 PM.

        Comment

          #5
          Re: P-Channel MOSFET testing

          Originally posted by Scenic View Post
          ^lol

          Now I just need to find a suitable replacement.. all I've found so far were TO220, not TO252.. (or I'd have to order 1k of them..)
          Too bad you don't live in the US:

          http://search.digikey.com/us/en/cat/...376381?k=40P03

          Um, nevermind, 2K minimum for TO252 version.
          Last edited by LLLlllou; 12-13-2011, 10:51 PM.

          Comment

            #6
            Re: P-Channel MOSFET testing

            In TO-220-

            eBay: http://stores.ebay.com/leemoom611

            http://www.ebay.com/itm/170744677931

            A little cutting and filing perhaps...?
            veritas odium parit

            Comment

              #7
              Re: P-Channel MOSFET testing

              Making a TO220 MOSFET fit shouldn't be a problem really..

              And i found that exact seller too.. That's the only option I have atm apart from buying 1k+ of the damn things lol
              One strange thing though.. the auction you linked to doesn't appear in his shop at all on ebay germany. Only the 5pcs and up ones.. weird

              PS: I love using that -smiley.. fits me so well

              Comment

                #8
                Re: P-Channel MOSFET testing

                I would message him via eBay and see what can be done. Easy to set up a 'private' sale via eBay for just you.

                >>PS: I love using that -smiley.. fits me so well <<

                Yes! Your original avatar was a classic, kinda like JunkParts' Bobble-head Bill. But, since only the 'upper crust' can have animated ones now.......

                I attached it here so it will remain on the board.



                Cheers!
                Toast

                PS: What/who is the manufacturer? Or, the complete number(s) on the device?

                .
                Attached Files
                Last edited by Toasty; 12-14-2011, 11:39 AM.
                veritas odium parit

                Comment

                  #9
                  Re: P-Channel MOSFET testing

                  I can view that auction just fine with the link you posted, but that auction just doesn't appear in his shop at all when I go there from ebay.de instead of .com.

                  My orignal avatar (the blinking text smiley i think (?)).. well.. I found it was kind of annoying/distracting. That's why i replaced it.
                  No need to attach stuff. My webspace isn't going anywhere
                  I've been using it for well over 5 years now. No problems apart from some small hiccups (server maintenance)

                  As for the original MOSFET..
                  There's no logo or anything on it. Only 2 lines of text, which are very faint.

                  40P03-20
                  AA8OAX (the O could be a zero.. not sure)

                  I've tried taking a photo of it, but after about 50 of them which turned out to be just a more or less blurry pixel-salad, I gave up. Below is the best i could manage. Ironically, my cellphone cam gave me much better results than my digital camera, as I'm able to manually set the focus.. lol



                  It looks like there's an underscore below the "40" and the "20"

                  Comment

                    #10
                    Re: P-Channel MOSFET testing

                    >>No need to attach stuff. My webspace isn't going anywhere <<

                    Yup. But now it's part of the boards and I have it bookmarked for my use...

                    There are so many situations where that is appropriate. hehehe

                    Use the "Ask the Seller a Question" link in the 5pc auction. See if he'll do what you need.

                    Toast
                    veritas odium parit

                    Comment

                      #11
                      Re: P-Channel MOSFET testing

                      I've already bought the 40P03's from that chinese seller. However.. looking through his feedback it seems most of the stuff takes about a month or so to arrive. With christmas in between, I kinda doubt I'd get it before january

                      So I went looking for what i could get locally (and hopefully faster).
                      One thing that turned up was a Vishay SUD50P04-13L-E3
                      Compared to the 40P03 datasheet, the specs look "close enough" from what I can tell.

                      Drain-Source breakdown voltage is 40V instead of 30V, continuous Drain current is max. 60A instead of 30A (at 100°C it would be 43A instead of 18A), and RDS on is 22mOhm instead of 28mOhm.
                      And to top it off, it's TO252 (like the original) instead of TO220.

                      Would that one be a good substitute
                      I've attached both datasheets.
                      Attached Files
                      Last edited by Scenic; 12-16-2011, 04:13 PM. Reason: forgot the datasheets.. *facepalm*

                      Comment

                        #12
                        Re: P-Channel MOSFET testing

                        You can always put it in and see if goes *BANG!!*...

                        It looks okay as a sub.

                        The others to watch are:
                        t/d (on & off)
                        t/r
                        t/f
                        t/rr

                        In this case the t/d(off) is double for the 50P04, but the other 4 are better than or close enough. Even a 100kHz switcher (10,000ns) is slow compared to that number (60ns).

                        Toast
                        Last edited by Toasty; 12-16-2011, 06:07 PM.
                        veritas odium parit

                        Comment

                          #13
                          Re: P-Channel MOSFET testing

                          I'd prefer not to damage it more than it already is :P
                          I've wasted enough time and money on that TV already.. sometimes thinking if i should just bash it to pieces with a bat for all the frustration it caused

                          I kinda doubt that MOSFET is all that's wrong with the PSU and I can pretty much forget about giving the TV to my mom for christmas anyways..
                          (I'm not like rich or something that I could just go and buy a (most likely crappy) new cheapo one for 350+euro (roughly 460usd))

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