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    #1

    LG 50PJ350-UB Power board problem

    Hello everyone! I just got what I hope is a good deal on a 2 year old 50" LG plasma. Using the training manual for this model I have determined the problem is in the power board. (I could not upload the training manual due to its' size.)

    The problem with the power board is that it will not stay on. When power is applied it will click on but will shut down about two seconds later, with a load or without one. It shuts down faster when the light bulb load tester I made is attached to it. The manual called for two 100W bulbs in series (200W load), I used two 60W in parallel that are in series with a 90W bulb (210W load). In the brief time it is on, all the necessary voltages are there and they seem to be at the correct level. The training manual says that with nothing but the AC power and the load tester connected (no main board) the power board should come up and stay on. I even tried forcing it on following the manual's instructions using jumpers and resistors and the results are the same, click on, click off.

    From what I have read it seems that IC701 is supposed to control all the functions and it seems to me that some kind of circuit protection is kicking in and shutting it down. I cannot find a datasheet for this IC which is a F4316MSF17, the only datasheet I could find was for another IC on the board, a L6599AD chip and I have attached it to my post. I figured if you could find out what could cause the protective circuitry to trip then it would narrow down where to look for the problem. I am hoping someone on the forum can point me in the correct direction to find the problem with this board as my searching has not turned up anything useful. I would like to post the training manual but the best I can do is to provide a link to the site where I got it.



    I will be very appreciative of any help you could provide.

    Thanks,
    Lloyd
    Attached Files
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    #2
    Re: LG 50PJ350-UB Power board problem

    I have downloaded the manual, but don't have time right now to look through it in any detail.

    Everyone has different styles in troubleshooting, but I like checking for steady and stable 5V standby. If the PS shuts down, then check all the fuses to see if any are open. Then I would check all the mosfets and diodes on the power board to see if they are shorted.
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      #3
      Re: LG 50PJ350-UB Power board problem

      It seems the fuses and diodes (including the zeners) are all listed on page 35. Your mosfets, schottky rectifiers, dual diodes will likely be mounted on the heatsinks.
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        #4
        Re: LG 50PJ350-UB Power board problem

        See if your board has a 6 pin chip labeled

        3BR1565JF

        on your board.
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          #5
          Re: LG 50PJ350-UB Power board problem

          Thanks for taking the time out to look at this. I did find another LG thread that has a similar power board and in it one of the posters mentioned a tech telling him that they had a problem with the big block resistors going bad. I checked R929 22 ohm 5W in the upper right hand corner and it was open. I had some 10 ohm 5W resistors on hand so to test it I replaced the open one with two of these in series. That was when the fun began....

          I was no longer getting a flash on my load tester at all nor was I getting any voltage readings that I had previously seen when testing the board. Odd was my first thought so I started checking and found fuse F801 blown where previously it was good on my prior tests. I replaced it and tried the board again and got the same result which was no output voltage (except for the 5VSB) however brief and a blown fuse unlike all my testing prior to changing the resistor. Then I remembered the "incident" I had earlier in the day.

          After testing the board per the manuals instructions and determining it was bad I decided to get some pictures for posting. It was overcast and I knew the lighting was only going to get worse so being impatient I did not wait long enough for the big caps to discharge. I received a nice tingle and the stainless steel pan I dropped it into got a arc mark. (I think it was from this board and not something previous.) So I do not know if this caused the problem on the primary side or not but I have a feeling it did. Following the fuse lead me to Q801 and Q802. I removed them both at the same time so I got them mixed up. One is completely shorted and the other is showing shorted between legs two and three. http://www.digikey.com/product-searc...0-5-ND&x=0&y=0 I checked around these two mosfets for more bad parts but everything else I pulled and tested from that area seemed OK.

          I am now in the process of testing the parts around R929 to see if any to them are bad. I want to try and get everything I need in one order but I have my doubts considering my track record for Digi Key orders.

          I will post back with what else I find suspect and thanks for taking a look at this. If you have any more suggestions I will do my best to try them.

          Comment

            #6
            Re: LG 50PJ350-UB Power board problem

            Originally posted by retiredcaps View Post
            See if your board has a 6 pin chip labeled

            3BR1565JF

            on your board.
            It does have this chip (IC301 in the middle of the center heatsink) as I saw the video and Ebay kit. The one on my board does not show any shorts and I am not sure how else I could test this chip. I would like to know for sure it was good so if there is another way of testing it I am all for it.

            Comment

              #7
              Re: LG 50PJ350-UB Power board problem

              Originally posted by LDSisHere View Post
              I checked R929 22 ohm 5W in the upper right hand corner and it was open. I had some 10 ohm 5W resistors on hand so to test it I replaced the open one with two of these in series.
              I don't have any formal training in electronics and hope to never apply Ohms law, but I wonder if (22 vs 2x10 in series) 2 ohms (10%) makes a difference or not? I'm guessing probably not, but I could be wrong?

              In any case, if you are going to place a digikey order, get a couple of 22 ohm 5W resistors. Digikey shipping prices are very reasonable and you get it fairly quick.

              so being impatient I did not wait long enough for the big caps to discharge.
              I hookup insulated aligator clips, one at a time, to the large cap and make sure it is below 5V DC before I touch anything.

              If you have any more suggestions I will do my best to try them.
              Since you shorted out a few components, I suggest systematically checking every component for shorted transistors, diodes, mosfets and open resistors/fuses. I suggest writing down each component as you test them on a sheet of paper to keep track of what was tested and what is suspicious and needs to be test out of circuit.

              Looking at the power board, I estimate it will take you about 30 minutes to check everything. You can't do anything else until the parts arrive.
              Last edited by retiredcaps; 12-07-2012, 02:57 AM.
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                #8
                Re: LG 50PJ350-UB Power board problem

                Originally posted by LDSisHere View Post
                The one on my board does not show any shorts and I am not sure how else I could test this chip.
                I have 2 at home. I tested both in every pin combination and there are no shorts between any of the pins. That is not a guarantee that it works, but at least it is not shorted.

                If it turns out that this IC is bad, I'll send you one.
                Last edited by retiredcaps; 12-07-2012, 02:58 AM.
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                  #9
                  Re: LG 50PJ350-UB Power board problem

                  One other suggestion while you are waiting/ordering for parts. I haven't worked on a plasma and tom66 is definitely the expert here, but you should check all your other sustain boards for shorts. In addition, check for blown fuses. For example, page 70 of the training manual has a procedure.

                  One other note. I believe plasmas have about 200V DC in all sorts of places so don't touch the heatsinks. Since you have 2 multimeters, I suggest you put the Fluke 21 with insulated aligator clips onto the legs of the big capacitor (make sure they are clipped on good) so it monitors the DC voltage at all times. Then when you power off or if the TV goes off by itself, you will have an idea if the large filter capacitor is charged or not.
                  Last edited by retiredcaps; 12-07-2012, 02:59 AM.
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                    #10
                    Re: LG 50PJ350-UB Power board problem

                    Originally posted by retiredcaps View Post
                    I don't have any formal training in electronics and hope to never apply Ohms law, but I wonder if (22 vs 2x10 in series) 2 ohms (10%) makes a difference or not? I'm guessing probably not, but I could be wrong?
                    I am not exactly sure how much difference it would make in the circuit myself but my thinking was that 10% difference was much less than an open circuit and had I not cause myself more problems would have allowed me to at least get the power board up and running to check other components.

                    Originally posted by retiredcaps View Post
                    In any case, if you are going to place a digikey order, get a couple of 22 ohm 5W resistors. Digikey shipping prices are very reasonable and you get it fairly quick.
                    They are on my list to order today. http://www.digikey.com/scripts/DKSea...04613049265743



                    Originally posted by retiredcaps View Post
                    I hookup insulated aligator clips, one at a time, to the large cap and make sure it is below 5V DC before I touch anything.
                    After the lesson I learned yesterday I will probably start doing the same. The short term pain was bad enough but having to buy and wait on parts that most likely were good before this incident occurred is the real punishment for me.



                    Since you shorted out a few components, I suggest systematically checking every component for shorted transistors, diodes, mosfets and open resistors/fuses. I suggest writing down each component as you test them on a sheet of paper to keep track of what was tested and what is suspicious and needs to be test out of circuit.
                    I have checked a lot of the board but I still have a few more items to go before I am satisfied. The one thing I am finding that is a real pain is for some reason, that is beyond my knowledge level, there is a lot of diodes connected in parallel with resistors. This makes diode checking a real chore as you have to de-solder it to test it. (I would love to know the purpose of this arrangement.)

                    Looking at the power board, I estimate it will take you about 30 minutes to check everything. You can't do anything else until the parts arrive.
                    I wish I could do it this quickly but I tend to de-solder anything I find suspicious for accurate testing (if it is something I know how to test) and this includes SMD parts. So far I have not found anything else that has tested bad.

                    Originally posted by retiredcaps View Post
                    I have 2 at home. I tested both in every pin combination and there are no shorts between any of the pins. That is not a guarantee that it works, but at least it is not shorted.

                    If it turns out that this IC is bad, I'll send you one.
                    Thanks, your offer is very generous. Digi Key does not seem to carry that part so getting one could be a pain. I really hope it is not a problem but I will have to get my other parts first to know for sure.

                    Originally posted by retiredcaps View Post
                    One other suggestion while you are waiting/ordering for parts. I haven't worked on a plasma and tom66 is definitely the expert here, but you should check all your other sustain boards for shorts. In addition, check for blown fuses. For example, page 70 of the training manual has a procedure.
                    Good idea, I have been focusing so much on getting the power board working that I have not given much thought to testing the other boards.

                    One other note. I believe plasmas have about 200V DC in all sorts of places so don't touch the heatsinks. Since you have 2 multimeters, I suggest you put the Fluke 21 with insulated aligator clips onto the legs of the big capacitor (make sure they are clipped on good) so it monitors the DC voltage at all times. Then when you power off or if the TV goes off by itself, you will have an idea if the large filter capacitor is charged or not.
                    Another good idea. I have found having two meters very handy in just the short time that I have had that luxury. (I did not consider the 113 a second meter, it was just a capacitor tester. )

                    Comment

                      #11
                      Re: LG 50PJ350-UB Power board problem

                      retiredcaps, you're spot on.... it's the 6 pin chip 3BR1565JF that's the culprit. I've created a repair kit to fix the LG 50PK models, but i've also noticed that the Infineon 3BR1565JF chip is also in the LG 50PJ models and some Zenith models.. I'm eager to know if the repair kit will work in those models as well

                      Repair kits NOW available on Ebay NOW! 50PK models
                      http://cgi.ebay.com/ws/eBayISAPI.dll...m=200855173187

                      Comment

                        #12
                        Re: LG 50PJ350-UB Power board problem

                        I have managed to make some progress on this on getting this TV working. Not as much as I would like however.

                        IC801 was directly connected to the two FETs I had shorted and was giving me some suspicious readings when I was testing it. The problem I had was that I did not know what would constitute correct readings. Since Digi Key had these chips in stock and it was cheaper than just one of the FETs I decided to order one just in case. This past weekend I found some FET's that had very similar specs as the two I had fried except they had a slightly lower Amp rating but everything else about them matched. I decided to temporary use them to see if I could get the supply to turn on again. With these in place the supply was still not turning on but it was no longer blowing the fuse like it had been when the shorted FETs were in the board. Today I received my parts and I replaced the FETs, IC801, and the 22 ohm 5W resistor. Unfortunately, I used my iron to desolder IC801 instead of my heat gun so I removed two "not connected" pads and tore two others as you can see in the pictures. Not good, but it could have been a lot worse and I did manage to get the new one soldered in place.

                        Per the manual I connected my load tester to the power board and left the connectors disconnected except for the AC power. The manual says doing this will cause the supply too start up all power outputs. As you can see in the picture the load tester came on and this time it stayed on unlike when it had the bad resistor and would go off immediately. So I am thinking problem solved but I was mistaken.

                        When the power board was connected back properly it would never get the the point where it would send the M_ON signal. I decided to go back to testing the power board moving from page 40 to page 41 of the training manual. Some of the voltages varied some from what the manual has listed on page 42 but the worst was the STBY when the power board was in actual STBY mode. In standby the Stby 5V is supposed to be 3.46V and it is then supposed to jump to 5.14V when the supply powers on. When I jumped pin 18 to ground to keep the supply off but in standby, the Stby 5V voltage would spike up to 5.33V and it would then start oscillating between 3.40V and 3.97V over a very brief period (1 to 2 seconds) and that is how it would stay until the supply was started. Once the supply was on, all the voltages were stable including the 5VSB at 5.187V. I was thinking the unstable standby voltage may be the cause of the main board not sending the turn on signal. So I decided to work on the 5VSB circuit.

                        The 3BR1565JF controls the STBY 5V voltage and works much like the Viper27 I have been experimenting with on PC power supplies. Bafury is correct that 3BR1565JF is hard to source in the US. Its' big brother the 3BR2565JF however is available from Mouser and the only real difference between them is that the 3BR2565JF can handle more load so I had ordered one to try if needed and luckily it arrived today also. Testing the resistance on the two of them out of circuit showed basically identical readings on every measurement which surprised me as I expected the 1565 to show differently as I thought it was the source of the problem. In addition to substituting the 2565 for the 1565 I changed diode D304 which is part of the current sense circuit. I then tested the standby voltage again to see the results of the new components in the supply. I was not expecting the results to be identical to when the 1565 was in the board, but they were. This tell me the 1565 is good but I may have a problem with the feedback circuit as I do not know what else could cause this type of voltage osculation.

                        Does anyone else have suggestions where to look for the source of this problem? Also am I correct in my thinking that the fluctuating standby voltage would prevent the TV from trying to turn on? Any help in figuring this out would be greatly appreciated.

                        Thanks,
                        Lloyd
                        Attached Files

                        Comment

                          #13
                          Re: LG 50PJ350-UB Power board problem

                          That whole board is toast, time to order a new one. You'll never be able to make that IC work after the pads have been ripped up like that. Looking at the photo it appears the legs are no longer making contact with the traces.

                          Comment

                            #14
                            Re: LG 50PJ350-UB Power board problem

                            BTW, two 60W bulbs in parallel plus one 90W bulb in series does not make a 210W load. The 90W bulb will be the limiter, so at best it will be 90W. If they work like resistors, it will be 51W.
                            Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                            For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                            Comment

                              #15
                              Re: LG 50PJ350-UB Power board problem

                              Originally posted by Cosmo66 View Post
                              That whole board is toast, time to order a new one. You'll never be able to make that IC work after the pads have been ripped up like that. Looking at the photo it appears the legs are no longer making contact with the traces.
                              The legs are making contact or else the power supply would not be able to run the load tester. the only two legs that are not making contact were not connected in the first place.

                              Originally posted by tom66 View Post
                              BTW, two 60W bulbs in parallel plus one 90W bulb in series does not make a 210W load. The 90W bulb will be the limiter, so at best it will be 90W. If they work like resistors, it will be 51W.
                              The manual said two 100W bulbs in series, the closest I had to that are 90W. I figured two 60W in parallel in series with a 90W was closer in range than two 90W in series. Either way it has nothing to do with the standby voltage osculating which is the current problem I need to resolve.

                              Comment

                                #16
                                Re: LG 50PJ350-UB Power board problem

                                Originally posted by LDSisHere View Post
                                the only two legs that are not making contact were not connected in the first place.
                                I stand corrected. I guess it will work. Good luck!

                                Comment

                                  #17
                                  Re: LG 50PJ350-UB Power board problem

                                  You may want to check the two green thermistors right below the relays. They act as circuit protection and can shut down a power supply. I had one that was cause of failure before, and now that I think about it I'm pretty sure it was an LG. It looks like there's a black one also off to the right between the coil and red connector. (Actually I think one's a thyristor and the other is a thermistor?? I always confuse the two)

                                  Anyways to check them you'll need to google the part number and see what the resistance should be out of circuit

                                  Comment

                                    #18
                                    Re: LG 50PJ350-UB Power board problem

                                    I think I may have found the cause of my unstable standby voltage, but I could be wrong.

                                    The voltage on the secondary side of the optoisolator was osculating from from 0 to slightly over 3V. I replaced the optoisolator and it made no difference. I temporarily replaced the KIA2431 with a KA431 all this did was make the voltage osculate at a higher voltage level.

                                    So I traced the circuit back to RL101 and RL103 where they measured the same resistance on both devices on the secondary side. When I measured the primary side I found RL103 had 15 ohms of resistance but RL101 showing an open circuit. I may be mistaken but I think they should be the same and this is what was causing the voltage to fluctuate. Is this a reasonable conclusion or am I completely off with my reasoning?

                                    http://www.digikey.com/scripts/DKSea...10358406538207

                                    Thanks,
                                    Lloyd
                                    Attached Files

                                    Comment

                                      #19
                                      Re: LG 50PJ350-UB Power board problem

                                      Originally posted by LDSisHere View Post
                                      I replaced the optoisolator and it made no difference.
                                      Optoisolator's rarely, but not never, go bad. I think I recall one bad one in almost 3 years of participation.

                                      When I measured the primary side I found RL103 had 15 ohms of resistance but RL101 showing an open circuit.
                                      Your link to digikey says part not found so I don't know what you are looking at.

                                      The Fluke 77 IV can read up to 60M ohm. Without knowing the part number, I can't be sure if RL101 is bad.

                                      Obviously, you should desolder the component (relay) and measure it out of circuit to verify.

                                      PS. Your pics are excellent. In addition, it helps a lot when you highlight the problem area so I don't have to spend my time searching for the component. I don't have selldoor's eyesight.
                                      Last edited by retiredcaps; 12-14-2012, 02:11 AM.
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                                        #20
                                        Re: LG 50PJ350-UB Power board problem

                                        Page 37 of the manual gives an explanation of how the relays (RL101 and RL103) works.

                                        Here is where multiple multimeters with aligator clips help with features like min/max to capture the possibly transient readings.
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