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Samsung UE48JU6400W - back light on, sound on, sometimes picture.

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    Samsung UE48JU6400W - back light on, sound on, sometimes picture.

    Hi Guys,

    This forum has been in great help to me, but I stumbled upon a strange problem with a salvaged Samsung TV that I am banging my head to troubleshoot.

    PSU: L48S6 FHS BN44-00807D
    T-Con: BN95-01937A
    Panel: CY-GJ048HGLVLH
    MB: NA (Currently as the TV is assembled and forgot to take picture)

    As I said earlier I have some issues with the TV I got from a friend of mine. The TV had no picture, but sound, back light and everything else was working fine.
    It was sent to an authorized service for repairs and returned with the diagnose that the LCD panel is dead.

    I took it, as I like to tinker with electronics and started troubleshooting it. Thought that i should give it a try by replacing the T-Con board.
    First the TV did not start, but after some tries picture came back and it was perfect. No artifacts or anything. TV seems to respond well to the remote, etc. I assembled it again and it was working for some time, but after powering it off from the remote and powering it back on the picture was gone again. After waiting for 5-10 minutes and then powering it back on the picture is back.

    What I have checked on the PSU:
    I have looked at the PSU board but did not find any visibly burnt components.
    I have measured the voltages on the test point on the transistors of the PSU. On the board it says that the Power on voltage should be 13V and it is present, but the standby voltage is 9V instead of 8V. Also there is a high pitched sound coming from the PSU when the TV is in standby mode.


    What I have checked on the T-Con:

    T-Con has two LEDs. When the TV is powered on one of the LEDs is constantly on, but the other one flashes for a second and then turns off. In the case where the panel works both LEDs are lit constantly.

    To sum everything up:
    1. Checked the PSU. Power on Voltage is 13V as expected, but standby voltage is 9V instead of 8. High pitched sound coming from the PSU board when in standby mode.
    2. Replaced the T-Con board. It has 2 LEDs which are constantly on when panel works fine. When the panel does not work fine one of them flashes for a second and goes off.

    Is it possible that these 9 volts during standby somehow mess with the TV so it does not really go into standby and mess the startup procedure of the TV?
    Since the panel works fine (when it works) I really start to doubt the diagnose from the repair service the TV was sent to.

    I am not really sure how to proceed further with the troubleshooting. Any help would really be appreciated.

    #2
    Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

    Have you tried to update it's firmware It may be worth trying.

    https://www.samsung.com/ie/support/m...E48JU6400WXXH/
    Willing to help but I'm no expert.

    Comment


      #3
      Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

      Originally posted by dick_barton View Post
      Have you tried to update it's firmware It may be worth trying.

      https://www.samsung.com/ie/support/m...E48JU6400WXXH/
      The panel stopped working again completely, and I am not able to bring it up again.
      I will try to manage and update the firmware blindly, but I am not sure if I will manage to get through the prompts. Or keep trying to start/restart the TV until the panel fires up again and then update it.

      I will later upload some pictures of the components if someone sees something that is not right.

      Comment


        #4
        Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

        Here are pictures of the internals of the TV
        Attached Files

        Comment


          #5
          Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

          What voltages do you have on connector CNM803
          Can you give the pin No., Pin Name, Voltage of each pin 1 - 12
          Pin 1 Fail Count = xxV
          Pin 2 ANA_DIM = xxV
          Pin 3 A13V = xxV
          etc

          What voltage do you have at the fuse on the Tcon
          What voltage do you have at the connector feeding the led strips
          Last edited by dick_barton; 05-15-2020, 01:02 PM.
          Willing to help but I'm no expert.

          Comment


            #6
            Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

            Maybe check your diodes on powerboard, meter in diode mode, should get a reading about .3xx to .7xx in one direction and OL or 1 when you reverse the leads.
            Last edited by nomoresonys; 05-15-2020, 01:41 PM.

            Comment


              #7
              Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

              Checked the voltages in standby and powered on state:

              Standby:
              1. FAIL_COUNT - 3.15V
              2. ANA_DIM - 0V
              3. A13V - 9.01V
              4. OD_ON/OFF - 0V
              5. A13V - 9.02V
              6. PWM_BLU - 0V
              7. A13V - 9.02V
              8. POWER_ON - 0V
              9. A13V - 9.02V
              10. GND - 0V
              11. GND - 0V
              12. GND - 0V

              Fuse on T-Con - 0V

              Powered on:
              1. FAIL_COUNT - 3.15V
              2. ANA_DIM - 3.38V
              3. A13V - 12.84V
              4. OD_ON/OFF - 3.33V
              5. A13V - 12.84V
              6. PWM_BLU - 3.29V
              7. A13V - 12.84V
              8. POWER_ON - 3.29V
              9. A13V - 12.84V
              10. GND - 0V
              11. GND - 0V
              12. GND - 0V

              Fuse on T-Con - 12.79V

              The regarding the power to the LED strips there are 4 wires:
              - 104V Black
              - 104V Black
              - 208V Black
              - 0V Grey

              I found three diodes on the board(except the one in the rectifier) all in all and they both measure fine.

              EDIT: All voltages are measured while the ground probe is connected to the LCD panel.
              Last edited by dronerat; 05-16-2020, 02:43 AM.

              Comment


                #8
                Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                I'm not sure of the Fail_Count but all the other voltages for "power on" appear to be OK including the backlight voltages. You have 12V on both sides of the fuse?

                So the backlights are working but no picture? Do you have sound?
                Last edited by dick_barton; 05-16-2020, 02:45 AM.
                Willing to help but I'm no expert.

                Comment


                  #9
                  Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                  Maybe try disconnecting the wi-fi board, see if tv works.

                  Comment


                    #10
                    Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                    Originally posted by dick_barton View Post
                    You have 12V on both sides of the fuse?
                    12.79V on both sides of the fuse.

                    Originally posted by dick_barton View Post
                    So the backlights are working but no picture? Do you have sound?
                    Yes. When I connect the coaxial cable channels are working and sound is coming out of the TV.

                    Originally posted by nomoresonys View Post
                    Maybe try disconnecting the wi-fi board, see if tv works.
                    No success.

                    It seems that the T-Con is trying to start, because the second blue LED flashes for a second when powering on the TV, but then the LED turns off and picture is not coming up. When the panel was working yesterday both of the LEDs were on constantly.

                    Per some guide I found I have also tried disconnecting the ribbon cables to the panel in order to at least get half of screen working, but nothing comes up.

                    When I disconnect one of the ribbon cables from the T-Con to the panel(it doesn't matter which one) the second LED on the T-Con does not light up at all.

                    Is there any way I can make this particular T-Con/Panel display test patterns?
                    Last edited by dronerat; 05-16-2020, 06:02 AM.

                    Comment


                      #11
                      Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                      I'm not aware of how you can set up any display test pattern on the Tcon.
                      Can you replace the tcon. They appear to be inexpensive.
                      Willing to help but I'm no expert.

                      Comment


                        #12
                        Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                        Originally posted by dick_barton View Post
                        I'm not aware of how you can set up any display test pattern on the Tcon.
                        Can you replace the tcon. They appear to be inexpensive.
                        I have already tried replacing the T-Con with little success. I got it to fire up sometime after replacing the T-Con but shortly after that it stopped working again.

                        I did some more investigation. Replaced the thermal paste on the T-Con and went on for the motherboard to replace the paste as well. I saw some test points and decided to give them a try(Pictures attached).

                        The test points for the EEPROM are at 3.3V which i believe is good.

                        I have measured CVBS_OUT and it gives 0.89V and the 5V point gives 5.13V and all other give 0(IMG_1519.jpg). Not really sure if it is OK.

                        The thing that bothers me is the SPI set of test points (IMG_1519.jpg) on the motherboard.

                        The readings there are as follows:

                        SPI_CS - 0.46V
                        SPI_MISO - 2.43V
                        SPI_WP - 0V
                        SPI_MOSI - 0.82V
                        SPI_CLK - 1.30V
                        SPI_GND - 0V
                        SPI_VCC - 3.29V

                        Shouldn't SPI_MISO and SPI_MOSI both have the same voltage levels? As far as I have read (for SPI communication) they should be between 2.5V-5V. SPI_MISO seems around that, but SPI_MOSI is far from 2.5V.

                        I have disconnected the T-Con board and measured again, but the voltage levels are the same.
                        Attached Files

                        Comment


                          #13
                          Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                          If you think it may be an EEPROM problem try freezing it with a can of freezer spray and then power up.
                          Last edited by dick_barton; 05-16-2020, 09:17 AM.
                          Willing to help but I'm no expert.

                          Comment


                            #14
                            Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                            Wonder if they sent you a bad tcon, maybe test both for proper voltage, some have clearly marked test points, some not so clear.

                            Comment


                              #15
                              Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                              Ok. I have put the old T-Con back. Left it unplugged overnight and somehow the TV Panel powered on again.

                              Both the LEDs on the T-Con are on now (picture attached).

                              I tried updating the firmware, but it says that there is no new version. As far as I read there is no way to downgrade the Firmware version to check if it is a Software issue.

                              I managed to enter the service menu and also took some screenshots.
                              I see one SMPS Fail detect in one of the diagnostic menus. This might be caused because I accidentally shorted one of the mosfets white taking measurements, but I have no way of knowing as I could not get into this menu before the accident.

                              Performed also some tests through the HW Test menu and the only abnormal thing I see is the HDMI Switch IC test that it lead to some strange picture being displayed. Currently I have all the eco features and auto power off disabled and it is playing Youtube videos just to see if it will turn off again while playing.

                              This TV is driving me nuts, but I still believe it is repairable.
                              Attached Files

                              Comment


                                #16
                                Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                                I think that confirms that they either sent you a bad tcon or you somehow got a incompatible tcon from them.

                                Comment


                                  #17
                                  Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                                  So you didn't see anything in the service menu that might relate to that fail_count? MUST be extra careful in service menu, it's not too hard to brick a tv from in there.
                                  Last edited by nomoresonys; 05-17-2020, 06:08 AM.

                                  Comment


                                    #18
                                    Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                                    Originally posted by nomoresonys View Post
                                    I think that confirms that they either sent you a bad tcon or you somehow got a incompatible tcon from them.
                                    I double checked the labels. There is only one difference which I believe has to do with the manufacturing date or something (Pxx marking on the T-Con). I mean that yesterday i put the old T-Con back after changing the thermal pastes and everything and it was behaving the same way with both T-Cons. Left the TV unplugged from the mains overnight and it turned back on. That is when it started normally.

                                    Since I needed to power it off from the remote to get to the service menu it powered on correct again. Had 2-3 power offs while looking through the service menu and one of them did not start correct, but the others did. Now I am afraid to power it off again as it may not power back on correctly.

                                    Originally posted by nomoresonys View Post
                                    So you didn't see anything in the service menu that might relate to that fail_count? MUST be extra careful in service menu, it's not too hard to brick a tv from in there.
                                    The only thing I see that might be related to the fail_count signal is this measurement (SMPS Fet Fail Detect 1 in file IMG_1530.jpg). If you have any other idea of what I can check in the service menu. Any diagnostics, etc. I will be more than happy to do so.

                                    Comment


                                      #19
                                      Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                                      Maybe do a factory reset while you have it working.

                                      Comment


                                        #20
                                        Re: Samsung UE48JU6400W - back light on, sound on, sometimes picture.

                                        Suppose it could be an intermittent eeprom issue??

                                        Comment

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