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    #1

    LG 42" plasma power supply voltage double normal

    I am working on a 42PC5D LG Plasma tv and after replacing the Y sus board and Y buffer board still having problems. At first the fuse was blown on the Y SUS. So I replaced it with another one(another y board) and the tv powered on for about 5 seconds showing just the color pixels lite up before tv cut itself off. The fuse blew on the new board also. The tv will stay on with the Ysus and Zsus boards disconnected. Sound works fine.
    So I started checking the voltages on the PS board. Sometimes the power checks fine and others it is double what its suppose to be. i tried to adjust the Vs pot and voltage goes down alittle but not enough. From 423 to 368 volts. Its suppose to be 192v. I am new to component repairs but am learning alot reading forums and such.
    What will cause the voltage to remain high is my main question.
    I could just replace the power board but that doesn't help me understand whats wrong with the broke one. Any help is appreciated.
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    #2
    Re: LG 42" plasma power supply voltage double normal

    Also the voltage to the sound board is high . 6v is 12v, 3.4v is 7v, 12v is 24v etc.

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      #3
      Re: LG 42" plasma power supply voltage double normal

      This is a picture of the PS
      https://www.badcaps.net/forum/attach...1&d=1363058055
      Attached Files

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        #4
        Re: LG 42" plasma power supply voltage double normal

        You probably have a multimeter that has a low/near dead battery, but there in no indication on the lcd. We get this at least once a week.

        Replace your battery with a fresh one and redo your readings. All readings should also be DCV.
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          #5
          Re: LG 42" plasma power supply voltage double normal

          In case you did not know, you should also have a load on the high voltage of the power supply for the voltage to run stabilized. For my LG plasma the training manual recommended two 100W bulbs in series. Also be very careful working with these as it take a while for the voltage to bleed off the capacitors.

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            #6
            Re: LG 42" plasma power supply voltage double normal

            You were right retiredcaps the meter battery was causing the high voltage readings. Now that the readings are correct coming off the power board I still do not understand why the tv cuts off with the ysus connected. I bought a used board off ebay and it tried to turn on when first connected but now tv cuts off after 2 or 3 seconds. Could it be the board I bought has problems also?
            I tried to get a voltage reading at the connectors when I first turned on the tv but barely get .1v and tv cuts off. I hear a wine in the chip on the ysus for a sec right before tv cuts off. Any thoughts as to what to check next?

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              #7
              Re: LG 42" plasma power supply voltage double normal

              I did get the 5v reading but no Va or Vs

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                #8
                Re: LG 42" plasma power supply voltage double normal

                The SMPS seems to be detecting a short and not turning on the high voltage power which is why you are not getting a voltage reading. It sounds like the new board may have been fine but you have a problem farther downstream that is blowing the Y-SUS. I have attached the training manual that should apply to this model. I would do the diode tests on pages: 41, 46, 47 and 48. You should also check the Z-SUS for shorts.
                Attached Files

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                  #9
                  Re: LG 42" plasma power supply voltage double normal

                  Thanks so much for the service manual. After doing the checks you suggested on my old and the new y buffer board it looks like both are bad. I will try to return the one I bought on ebay for a refund and buy a different one and see if that works.

                  Haven't checked the Ysus yet. Now I have my doubts as to wheither its good either. Too late to return that one ifs its bad. Checked all the voltages per service manual on the SMPS and all are present at the connectors. Hard to get good repaired boards these days. I try to buy boards from tv's with broken screens as they seem to always work compared to buying rebuilt ones.

                  Again thanks for the help. I enjoy reading these post on badcaps.

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                    #10
                    Re: LG 42" plasma power supply voltage double normal

                    I have had really good luck with getting parts from this place: http://www.retechtv.com The only problem is if they may not have the parts in stock. I would also do a diode test on any "new" parts before installation.

                    If your Y-SUS only has blown FETs and diodes you may can replace them yourself, you may can even scavenge enough good ones from one YSUS to fix the second one. This of course depends upon a lot of variables including your tools, abilities and time, not to mention the extent of damage to the boards.

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                      #11
                      Re: LG 42" plasma power supply voltage double normal

                      One question I have is about checking for shorts. Having trouble figuring out what is suppose to show readings and what is not. On the y sus board 5v and Va are not reading to ground but Vs is. Which is correct? I can solder with no problem and have bought and use a ESR meter to check caps. Checking fets, mosfets and voltage regulars are a bit tricky. Not sure which are which just looking at the numbers on them. No problem checking diodes and transisters

                      Comment

                        #12
                        Re: LG 42" plasma power supply voltage double normal

                        Originally posted by Glenn022 View Post
                        You were right retiredcaps the meter battery was causing the high voltage readings.?
                        Just out of curiosity, what brand and model number of the multimeter?
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                          #13
                          Re: LG 42" plasma power supply voltage double normal

                          Its a $20 cheap Performance Tool W2974. Bought it for car repairs and household use. I know I need a Fluke but can't spend extra right now for more tools with my son having shoulder surgery next month. And I am only one making any money so fixing tvs has to be cheap lol. Found this one by the road so working on it to learn. changing boards is easy way but cost way more so trying to learn how to replace components. My 80 year old about blind mother is still using a 25" CRT tv with tube about to go out so this would be the nicest tv she has ever had if I can get it working.

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                            #14
                            Re: LG 42" plasma power supply voltage double normal

                            Originally posted by Glenn022 View Post
                            My 80 year old about blind mother is still using a 25" CRT tv with tube about to go out so this would be the nicest tv she has ever had if I can get it working.
                            My local kijiji (like craiglist) has ads from people, almost daily, giving away 32 to 34 inch Sony CRT TVs (like the high end trinitrons not that long ago) for free.
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                              #15
                              Re: LG 42" plasma power supply voltage double normal

                              Originally posted by Glenn022 View Post
                              Its a $20 cheap Performance Tool W2974.
                              The reasons I asked are

                              1) I'm studying how multimeters work and how they are designed as a hobby.
                              2) Nowadays I'm more interested in the test equipment used to repair things than the actual repair itself.
                              3) I'm keeping track of the multimeters that don't display low battery warnings properly.

                              Obviously, you have your $$$ priorities in order so I'm not going to suggest that you get a Fluke or anything like that.

                              The Performance Tool W2974 is just a generic 830 multimeter that you find on ebay for $5 + free shipping. I have 4 of them at home. 3 are non working and 1 is working, but I never use it.

                              The 3 non working ones are the ones I'm trying to repair and learn mor about. I suspect 2 have bad CPU ICs and the other one has a bad voltage divider front end.
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                                #16
                                Re: LG 42" plasma power supply voltage double normal

                                Originally posted by Glenn022 View Post
                                One question I have is about checking for shorts. Having trouble figuring out what is suppose to show readings and what is not. On the y sus board 5v and Va are not reading to ground but Vs is. Which is correct? I can solder with no problem and have bought and use a ESR meter to check caps. Checking fets, mosfets and voltage regulars are a bit tricky. Not sure which are which just looking at the numbers on them. No problem checking diodes and transisters
                                I do not think VS should read shorted either in ohms mode or diode mode. If I am not mistaken, VA just passes through the YSUS on the way to the ZSUS board. You may want to check the ZSUS board and make sure it is not shorted also.

                                Checking FETs can be difficult. This link may give you some help in that area: http://www.allaboutcircuits.com/vol_3/chpt_5/3.html

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                                  #17
                                  Re: LG 42" plasma power supply voltage double normal

                                  Yes the Z sus gets its power from the Y sus on this tv. Some plasma tvs have the connectors to each board feeding off the power supply but not this one. I am trying to get this tv to turn on without the zsus even plugged in. Tried it both ways and still tv cuts off in 2 seconds.

                                  The fuse is not blowing anymore on the Y sus. The sound works without the cable screwed in now but with it attached there is no sound which worked a few days ago. The service manual says the last step to turn on the Vs and Va voltages comes from the main board at the vs on pin on the SMPS. Not getting a voltage reading there so starting to believe I have problems on more boards than ysus and y buffer. I ordered another y buffer so next week I will try again and see what happens. The voltage to a couple spots to the main board are reading 4.5 and 4.8 volts now which call for 5v. Wondering if the SMPS board has problems. One pin calling for 3.4v is 5v. Doesn't sound good.
                                  Unless this battery I replaced on my DMM has gone bad already and reading high again lol. Cheap meter may be blowing through batteries. I also noticed the temp leds on the control board are not lighting up at all. There is 4 of them. Unstable voltage can cause alot of problems in a circuit. Kind of lost as to what to do next.

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