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LG 23LS7D - DOA nothing.....

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    LG 23LS7D - DOA nothing.....

    A young mother brought this on in a bit ago. Power jack was broken and had pulled out (kids) It had also shorted against the earth grounded metal chassis.

    No fuses were blown. When i went to repair the jack I saw this board...(see pics) There were 2 badly swolen very cheap 10v off brand caps (also pic). One was total failed the other was almost gone. i noticed that there should have been a 25v or 35v in that position.
    Brain fart - what to do now? It is a piece of crap old clunker by my standard. However this gal obviously has little or no money and came to us off a referral and a little hope i could fix the cord right. I decided to replace the bad caps while i was in it with some equal value 50v i had. So i fixed the broken power cord jack and the caps... now as i look it is obvious that someone did those cheap crap 10v caps recently... then i see more evidence like screws loose still a couple in the wrong spots and such.
    I put the board back in (good fuse) but nothing still dead as a hammer.
    Dilema - try to fix it or return it to her with no charge.
    I hate these types because they are hard to test since the front comes off and the screen lifts out to get to the back.
    I think it is so old some of you vets may be familiar... I decided to give it a few minutes of my attention since even a little money is better than none..
    Attached Files

    #2
    Re: LG 23LS7D - DOA nothing.....

    I would also replace those small value caps 10uf 22uf etc. in the primary circuit, Its a good chance they are bad but being small usually won't bulge or show signs of leakage

    Comment


      #3
      Re: LG 23LS7D - DOA nothing.....

      If they put in the wrong voltage caps, how do you even know if they were the right uf value?

      Comment


        #4
        Re: LG 23LS7D - DOA nothing.....

        Bigger problems still bro... there is no voltage getting to the isolation coil from the mains side. I have the 120V up to the rectifier one of the heat sink mounted 4 leg jobs. It gets very tight and hard for me to trace from there so i took a quick break.. shaky hands and all LOL (I hate these types) So I now know the trouble is in the mains (hot) section of the PS. Gonna take a quick look for a schematic.
        R_J i'm with you but i already swapped out all the 10v caps. that is a before pic. I also tested all of them with my fluke and they are well within tolerance in circuit... dosen't mean it's a done deal though. Take an inch take a mile sort of thing here or better description... rabbit hole!! LOL
        I need to get the voltage over to that side. This board is literally baked brown...
        I guess i'll feel good if i can fix it as well as helping someone out a bit.

        Comment


          #5
          Re: LG 23LS7D - DOA nothing.....

          Originally posted by jetadm123 View Post
          If they put in the wrong voltage caps, how do you even know if they were the right uf value?
          you can see a couple of the originals they didn't change... 2200uF is what they were. Plus they're filter caps so are not too essential size wise within reason.

          schematics are always a plus though. (I am all for using exact precision sizes but on one like this i'm not going to worry much)

          Comment


            #6
            Re: LG 23LS7D - DOA nothing.....

            Here are two service manuals I was able to download for this model... I failed the electrical test so i am not qualified to get more than 3 downloads per day... LOL every time i miss one question... I am a super genius. I think it may be the what type of LED TV is already available.. i put LCD with LED backlight... other answers are LCD with CCFL back light, LED pixels, and OLED pixels. Do you guys know the answer?
            Attached Files

            Comment


              #7
              Re: LG 23LS7D - DOA nothing.....

              So was the bridge rectifier good?
              I assume no responsibility for any stupid suggestions I might post.

              Comment


                #8
                Re: LG 23LS7D - DOA nothing.....

                Originally posted by dskall View Post
                So was the bridge rectifier good?
                Yeah i just checked that again.. i have 166v DC comming out then it gets tight and crazy past there. There is nothing getting to the two big filter caps. I am going to discharge it and do a component test in the section i've narrowed it down to. there are a couple of IC's in there that I'm nervous about.. i blew one just like it literally to pieces on a different power supply. It's the layout and position of the board along with my shaky hands. It seems like a short but may be an open so I may be able to locate it cold. (the fuse doesn't blow)

                Neither service manual has the schematic for the PS... they just run on air... LOL Tesla TV!!!

                Comment


                  #9
                  Re: LG 23LS7D - DOA nothing.....

                  Boy i sure am going to a lot of trouble for what basically is a charity job....
                  LEARNING = VALUE
                  OK Here's what I found so far.... U500 (datasheet attached) Pin 3 is CS = current sense Detector. It shuts off the power ***BING*** when it gets too saturated. there is a Series resistor to CS as well as a protection diode. That diode and resistor is reading dead short. I suspect the resistor it is black. Diode is ZD502 Resistor is R512 (i do like that they marked the parts on both sides of the board) New problem I do not know what value that resistor should be can't see the ring colors anymore. Gonna pull it now...
                  Attached Files

                  Comment


                    #10
                    Re: LG 23LS7D - DOA nothing.....

                    OK diode is good... that resistor reads 1.3ohm out of circuit
                    DAMMIT it is marked on the bottom in white writing 1.2ohm.. putting her back in now... crap..
                    Last edited by Doc38343; 08-01-2017, 04:33 PM.

                    Comment


                      #11
                      Re: LG 23LS7D - DOA nothing.....

                      Well nothing wrong with a little charity once in a while
                      I assume no responsibility for any stupid suggestions I might post.

                      Comment


                        #12
                        Re: LG 23LS7D - DOA nothing.....

                        Originally posted by Doc38343 View Post
                        OK diode is good... that resistor reads 1.3ohm out of circuit
                        DAMMIT it is marked on the bottom in white writing 1.2ohm.. putting her back in now... crap..
                        out of circuit testing is only way .. check schem . you might have been able to see a low value resistor causing bad readings ..
                        wild guess u500 is bad ..

                        Comment


                          #13
                          Re: LG 23LS7D - DOA nothing.....

                          Check resistor FR500, 2.2 ohm. The voltage for the ic is supplied from + of the cap C150 through fr500, looks like there is another resistor r??? then through D501 to pin 5 of the ic, if the ic shorted I suspect fr500 is open
                          You should be getting 160 volts across the main capacitors, even if the ic is not working
                          Here are a couple pictures that might help, From Shopjimmy
                          Even two of the caps in the sj photo are bad (domed)
                          Attached Files
                          Last edited by R_J; 08-01-2017, 05:29 PM.

                          Comment


                            #14
                            Re: LG 23LS7D - DOA nothing.....

                            a schematic would be nice... found everything but that.
                            Down to looking at the mosfet and the 5501a that controls it.
                            popped out of one rabbit hole and heading down another!LOL

                            Comment


                              #15
                              Re: LG 23LS7D - DOA nothing.....

                              Originally posted by R_J View Post
                              Check resistor FR500, 2.2 ohm. The voltage for the ic is supplied from + of the cap C150 through fr500, looks like there is another resistor r??? then through D501 to pin 5 of the ic, if the ic shorted I suspect fr500 is open
                              You should be getting 160 volts across the main capacitors, even if the ic is not working
                              Nail on the head.. so does that mean the IC is shot??
                              resistor is reading 1.8M second time just OL...sure as crap aint 2R2

                              Comment


                                #16
                                Re: LG 23LS7D - DOA nothing.....

                                Yes, I suspect the mosfet in the ic is shorted, check the ic between pin 3 cs and drain 4-5

                                Comment


                                  #17
                                  Re: LG 23LS7D - DOA nothing.....

                                  Originally posted by R_J View Post
                                  Yes, I suspect the mosfet in the ic is shorted, check the ic between pin 3 cs and drain 4-5
                                  I got 3.6M there no short there... 4 and 5 are on the same rail

                                  Could the failed caps I found on the secondary side have just put too much on that resistor?
                                  You can see how hot the board had been running from the discoloration.

                                  Comment


                                    #18
                                    Re: LG 23LS7D - DOA nothing.....

                                    It's possible, replace the resistor and you'll find out if the ic's ok, Check Q450 & Q451
                                    Last edited by R_J; 08-01-2017, 06:01 PM.

                                    Comment


                                      #19
                                      Re: LG 23LS7D - DOA nothing.....

                                      Looking for a donor right now I can't tell if its a 1 watt or a half watt.. it was the ceramic hard type so i think it is a half watt...

                                      Comment


                                        #20
                                        Re: LG 23LS7D - DOA nothing.....

                                        OK R_J ... how did you know about that resistor. Is that an experience thing, like a common area to fail in SMPS or was there something more I could learn to do the same?
                                        Perhaps just putting in the time paying the dues (experience)?

                                        Comment

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