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LG55UB850V no picture or audio - flashing LED's help please?

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    #41
    Re: LG55UB850V no picture or audio - flashing LED's help please?

    MAN.. plug the socket CN5 correct tight on the T_CON !!!! it look at photo its out

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      #42
      Re: LG55UB850V no picture or audio - flashing LED's help please?

      I can assure you the connector at CN5 is fully plugged in and fully engaged. It just looks like it isn't in the picture - it's the design of the plug that makes it look like it is only half way in! But it is definitely clicked fully in place.



      So I have tried as you suggested. TV in standby, with probe at either J71 or J75, and as I turn the tv on with the RC the voltages appear as either 12v or 24v respectively. I then turn the tv off with the RC and the voltages drop back down to 0v. So the RC is working correctly.
      However, when I turn the tv on with the RC from standby, after the 3 slow red flashes, when the tv should be powered on, when I press IN_STOP on the service RC followed by 0413, nothing is happening. The TV does not seem to be carrying out the IN_STOP reset, and the voltages on J71 and J75 remain. The tv does not carry out the reset and go back into standby like it should.

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        #43
        Re: LG55UB850V no picture or audio - flashing LED's help please?

        did you by mistake used service remote power only before ?? it sound to me its power only. so üut the tv in standby and use the Service Rc power only... screen will be black.. messure 12 /24v and T-CON F1 then with same RC press exit. and plug the tv out from wall socket.. then dont use service RC just original one.

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          #44
          Re: LG55UB850V no picture or audio - flashing LED's help please?

          Yes I did use the power button on the service RC instead of the normal RC. I have followed your instructions, and then turned the tv on from the standard RC. Once the 3 red status LED flashes had finished and the LED had gone out, I tried again with the service RC pressing IN_STOP and 0413 but still nothing happens. No reset takes place and the voltages remain at 12 or 24v on those test pins.

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            #45
            Re: LG55UB850V no picture or audio - flashing LED's help please?

            still there are misunderstanding... however the voltage on T-CON F1 (Panel VCC ) fault we need to know who cause it.

            the LVDS cable (51 pin or more ) between MB and T-CON disconnect it from MB side. the last 3 or 4 pins (if they are 51 mean 51 50 49 48 ) are connected together and they are transfer the 12V from MB to T-con. put yours DM on one of them and turn on see if go for short time 12V or not

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              #46
              Re: LG55UB850V no picture or audio - flashing LED's help please?

              The 51 pin LVDS cable pins 48, 49, 50 and 51 all show the same voltage when the TV is powered on from standby. They do not show 12v at any point, nowhere near, they only show a tiny 0.08v! When the tv is first turned on from standby, the reading on these pins on the MB side starts at 0.035v and then over the space of around 10-15 minutes with the tv in the 'on state, the voltage only increases up to 0.085v

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                #47
                Re: LG55UB850V no picture or audio - flashing LED's help please?

                put every things back. you need to check on the power socket at the MB after turn on if you have on PIN 12 &14 (12V ). and on PIN 18 & 20 & 22 ( 24V )

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                  #48
                  Re: LG55UB850V no picture or audio - flashing LED's help please?

                  Do you mean check the readings on those pins on the 24 pin power socket on the logic board arrowed here?

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                    #49
                    Re: LG55UB850V no picture or audio - flashing LED's help please?

                    yes

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                      #50
                      Re: LG55UB850V no picture or audio - flashing LED's help please?

                      Ok thanks. So yes I am getting PIN 12 &14 (11.71V ) and on PIN 18 & 20 & 22 ( 24.12V ) so the logic board is receiving the correct voltages from the power supply board.

                      I have noticed that with the LVDS cable plugged into the logic board, pins 48,49,50 and 51 show 0.835v.
                      With the LVDS cable unplugged from the logic board, pins 48,49,50 and 51 show 0.085v.
                      So having the T-Con connected via the LVDS cable results in an increased voltage on pins 48,49,50 and 51, however still not the correct 12v - nowhere near.
                      Does this indicate a fault on the logic board in that case?

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                        #51
                        Re: LG55UB850V no picture or audio - flashing LED's help please?

                        ok good,,, now the last things you can do.
                        on the main boards we do have 2 micro switch its button to the top one near to right side the power socket you just measure it this is force reset DC. and the other to the right side of the socket where it goes to IR section this micom reset.

                        so while the tv off first try the first press and keep press while you turning on... if nothings change turn off and try same way the second one. it mean you press about 10 seconds each. and each time you did for one of them, try turn on again normal to see if there any change
                        Last edited by Diah; 01-29-2022, 12:26 PM.

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                          #52
                          Re: LG55UB850V no picture or audio - flashing LED's help please?

                          if above didnt brought any change .. then you need to make your last things to be sure nothings happened to the T-CON or the panel during you put it back together,, if some things drooped down under the T-CON or on the panel buffer boards. so first take the t-con out and inspect the downside. if clean. then need to disconnect the ribbon cable between T-con and panel ( from t-con side ) one by one each time and turn on. check if fuse (F1) increase to 12V or BL lit on. or the screen show half screen white. if nothings from above happened.. then Main boards defect.. sorry i don't have other good news for you. end from my side.

                          Comment


                            #53
                            Re: LG55UB850V no picture or audio - flashing LED's help please?

                            I have tried as you suggested, however sadly it made no difference.
                            I tried both SW3000 (MICOM_RESET_SW) and SW1901 URSA_RESET), holding in until the tv should have been on, but after testing the voltages and behaviour, nothing has changed.

                            I will take the T-Con board off and check there is nothing behind it that shouldn't be, and check each of the connectors and try turning the tv on after each check and report findings here.

                            Thank you for taking so much time to help me Diah, I really appreciate all your efforts and guidance.

                            I will look for a replacement logic board, and in the meantime, perhaps try my heat gun on the main logic board chips that use a BGA mounting, heating on top and underside the board, in an attempt to heat up the solder balls and try to reflow just to see if it makes any difference. If it does, it may be worth getting the board properly reflowed on those chips, if it turns out that's what the problem is. I would much rather rescue this TV than have to replace it but it will come down to cost...

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                              #54
                              Re: LG55UB850V no picture or audio - flashing LED's help please?

                              Originally posted by Scoff View Post
                              Thank you for taking so much time to help me Diah, I really appreciate all your efforts and guidance.
                              this TV than have to replace it but it will come down to cost...
                              Thank you too for following up.. but before you go to due the dirty work BGA / .. did you remember what did you watched / on which source at time power cut while the TV was on this could help to narrow the section specially it worked again after remove WIFI load,

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                                #55
                                Re: LG55UB850V no picture or audio - flashing LED's help please?

                                one little story i would like to add to the reader... some time very little thinks you would never expected happened guide you to hard work maybe with out end. so one time i was working on LG OLED. for diagnosing power on issue.. it drive me really to lost my mind.. at the end and just by chance i found the TV power on and it work perfectly.. i looked around what i did to let this happen... at the end i discovered one of my LG RC was the power button stick on contact so in room was always command turn off on-- from that day any RC i didn't need to use will be empty from batteries.. small matter with big issue .. thanks for reading and be aware.

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                                  #56
                                  Re: LG55UB850V no picture or audio - flashing LED's help please?

                                  Diah just been reading your replies so on this set you are saying its a mainboard issue is the bluetooth/wi fi module ok? im still learning myself so some great fault finding tips in this thread.

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                                    #57
                                    Re: LG55UB850V no picture or audio - flashing LED's help please?

                                    Originally posted by vinceroger69 View Post
                                    Diah just been reading your replies so on this set you are saying its a mainboard issue is the bluetooth/wi fi module ok? im still learning myself so some great fault finding tips in this thread.
                                    right now the MB defect because he measure the pin on the sockets there are 12V. &24V but after no include panel_VCC 12V. or USB 5.V it sound to me there are no command come from main IC to turn on other parts of Dc to DC ( look like same if some one pressing on service remote P.ONLY) --diagram at S.M page 31.
                                    Attached Files
                                    Last edited by Diah; 01-30-2022, 06:38 AM.

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                                      #58
                                      Re: LG55UB850V no picture or audio - flashing LED's help please?

                                      Originally posted by Diah View Post
                                      one little story i would like to add to the reader... some time very little thinks you would never expected happened guide you to hard work maybe with out end. so one time i was working on LG OLED. for diagnosing power on issue.. it drive me really to lost my mind.. at the end and just by chance i found the TV power on and it work perfectly.. i looked around what i did to let this happen... at the end i discovered one of my LG RC was the power button stick on contact so in room was always command turn off on-- from that day any RC i didn't need to use will be empty from batteries.. small matter with big issue .. thanks for reading and be aware.
                                      That brought a smile to my face - sorry you had to go through all that frustration. I'm sure you can look back and smile about it now!
                                      Trying to source a replacement board - all sites I've looked at are out of stock for used boards with this exact number. I've got a smaller spare tv I can use in the meantime, and would like to learn some more through reading online to see If I can narrow down the issue on my board, and confirm as suspected, that the issue lies with the main IC, or BGA solder connections underneath it.
                                      Where the various 12v pins on the logic board connector join together, is this what is referred to as the 12v 'rail'?
                                      Is it possible to follow this track to the main IC, testing the components along the way, to confirm that the 12v is at least getting to the IC?

                                      Comment


                                        #59
                                        Re: LG55UB850V no picture or audio - flashing LED's help please?

                                        Originally posted by Scoff View Post
                                        Is it possible to follow this track to the main IC, testing the components along the way, to confirm that the 12v is at least getting to the IC?
                                        12 & 24 you have them on the socket you linked now. main IC work with 3.3V and this will be taken from STBY one. the firmware start up script will command the main IC after power_ DET say yes we have 12 24. so the main will start send the command to other DC to DC to provide 1V 2.5V 1.5V 12Vpanel vcc all will taken from main 12V line, 5V which we said optical port or USB will taken from the 24V main line.

                                        as we have 12V and 24V stable at the socket.. mean we don't have any short circuit on MB ( this is good news )
                                        remain the main issue we have fault at firmware start script don't go to end to let the main IC complete the boot. (this why you can turn on and turn off via RC ... as this action belong to first start script ) but (you cannot send IN_STOP... as this action belong to last script boot complete )

                                        we need to find way to trick it.. for example use service remote P.ONLY to turn on ... then press exit after it switch 12 & 24 on .... or too this can help to avoid any glitch at firmware. freezing the ICs.

                                        Comment


                                          #60
                                          Re: LG55UB850V no picture or audio - flashing LED's help please?

                                          Ok so I have made some progress - I have managed to get the screen to come back on!
                                          I believe I have confirmed a solder issue on one of the chips.

                                          With everything connected and the tv in standby mode, I used the user RC to try to power the tv on. After the 3 red front status LED flashes, and the red LED went off, I left it in this state - where the tv should be 'on'.

                                          I measured the voltage at F1 and still only 0.085v.
                                          I used my heat gun on the low setting and gently moved it around, starting with the chip nearest the LVDS connector.
                                          Not expecting to achieve much, I didn't remove the white plastic covering that sits on top of the chips and covers 3 of them (is this a type of heatsink?), and just heated around the edges from a safe distance.

                                          Immediately while aiming the heat gun around one of the chips, I noticed the red LED on the board LD1900 starting to light up very faintly. I moved the heat gun away form the chip, and LD1900 gradually faded off again. Moved the heat gun back around the chip and LD1900 started getting brighter again. I kept the gun there for a couple of seconds until LD1900 reached full brightness, and moved the heat gun away, and LD1900 stayed lit this time. This LED is only normally on when the screen is on - however the screen wasn't on.
                                          I decided to power off the tv with the user RC, and try turning it on again with the user RC, and lo and behold, LD1900 came on and then so did the screen!

                                          I am looking at the service manual to try to identify this chip, the letters down the side go form A to T, but all I can see on the board is IC2.... as it is covered by the white plastic (heatsink?).
                                          Now when checking, I have 11.39 to 11.49v at fuse F1 - this voltage bounces repeatedly from 11.39 up to 11.49 and back to 11.39, then back to 11.49 etc.
                                          Also, the T-Con board is making a slight croaking noise (sounds like a frog quietly croaking!) which comes and goes every 2 seconds, and seems to coincide with the F1 fuse voltage fluctuating between 11.39 and 11.49v - perhaps because the T-Con board is not receiving full 12v?

                                          I very much doubt this is an actual 'fix' however I think I may have identified the faulty IC solder issue. I doubt I had enough heat in the short time to melt the solder under this chip, but perhaps it was just enough. I did nothing else, other than heat this chip and the duration/amount of heat gave a direct result by lighting up LD1900 LED by varying amounts.

                                          While the screen was on I was able to perform an IN_STOP reset successfully, however this hasn't changed the slight voltage fluctuation at F1. Everything is plugged in including the WiFi module currently and the tv 'seems' to be working..









                                          A video if the link works...

                                          https://photos.app.goo.gl/Y1DVTvDberPu66wy8

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