Panasonic LED TV TC-40A420U - Replaced Backlight LEDs but now no image/display or garbled

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • signal.quest
    Senior Member
    • Oct 2020
    • 50
    • United States

    #1

    Panasonic LED TV TC-40A420U - Replaced Backlight LEDs but now no image/display or garbled

    I have a Panasonic LED TV TC-40A420U. The TV was given to me as an attempt to fix or throw out. I replaced the Backlight LEDs and now the screen lights up, but there is no image/display. If I play with the up/down buttons I can get the display to change from black to garbled. I can't get sound from HDMI but not sure of what input is selected. I have no remote control. When I connect a laptop to the HDMI ports it recognizes a Panasonic TV for display and sound output but I can't see or hear anything through the TV. This makes me think the mainboard is OK, but not sure if mainboard can partially fail? I am hoping it is not a panel issue, but maybe I damaged it by dismantling all of the layers. It was my first attempt at LED backlight repair. I also was delicate with the panel circuit board, but I am concerned about it. Please see the pictures for what display shows. Any help is appreciated. Thanks.
  • signal.quest
    Senior Member
    • Oct 2020
    • 50
    • United States

    #2
    Some additional information:
    Panel is Innolux v400HJ6-ME2 Rev C1

    Logic/Mainboard/A Board:
    TXN/A1YZUUS (TNP4G565)

    Power (P) Board:
    TXN/P1AEVUS (TNPA6029)

    Please help me verify Panel or Mainboard is OK. Thanks.

    Comment

    • Diah
      Badcaps Legend
      • Feb 2013
      • 6353
      • Germany

      #3
      show us the back of the tv of all boards to see how they are connected to each other

      Comment

      • signal.quest
        Senior Member
        • Oct 2020
        • 50
        • United States

        #4
        Thank you for the reply. I am in process of checking the panel board for obvious issues, therefore it has been partially disassembled. But I have connected it back to show the critical connections (not speakers or indicator light). Thanks. Please see the photos. Thanks.

        Comment

        • Diah
          Badcaps Legend
          • Feb 2013
          • 6353
          • Germany

          #5
          under good magnifier check the contact pins of the LVDS cable at main boards side
          the one to panel with red and yellow mark need to check if there any cut at the cable side..
          the other U ribbon on panel buffer boards ( yellow ) check the contact pins too.
          Click image for larger version

Name:	image_331474.jpg
Views:	205
Size:	1.46 MB
ID:	3239985

          Comment

          • signal.quest
            Senior Member
            • Oct 2020
            • 50
            • United States

            #6
            I just checked all connection cable contact pins with a jeweler loop and I don't see any problem areas. The cable does has 2 bends/crimps in it that you can see from the photo. I suspect it was always like that but it is possible it got crimped when I had the TV dismantled and laying for weeks waiting for replacement LED shipment to arrive. Is there a way I can verify there are no breaks in the cable using a meter? Are those bends/crimps common or does it look like I made a mistake? Thanks.

            Comment

            • signal.quest
              Senior Member
              • Oct 2020
              • 50
              • United States

              #7
              Here are the photos of the crimped/bent cable.

              Comment

              • Diah
                Badcaps Legend
                • Feb 2013
                • 6353
                • Germany

                #8
                the crimped/bent cable.are normal,way to use for changing cable direction.

                you can try just disconnect the 2 on the right side of the U ribbon ( yellow mark ) and turn on the tv,, see if the screen will display half picture

                to check cable with DM. need to set the DM on peep ton option and check the pins of the socket from MB to panel one by one for connectivity

                Comment

                • Diah
                  Badcaps Legend
                  • Feb 2013
                  • 6353
                  • Germany

                  #9
                  this look for me Damage at LVDS
                  Click image for larger version

Name:	image_331484.jpg
Views:	186
Size:	2.74 MB
ID:	3240035

                  Comment

                  • signal.quest
                    Senior Member
                    • Oct 2020
                    • 50
                    • United States

                    #10
                    Thanks. I will try that test. Do you think my logic (A) board is OK since it is recognized when laptop is connected to HDMI? Is there any other way to verify it is OK?

                    Comment

                    • Diah
                      Badcaps Legend
                      • Feb 2013
                      • 6353
                      • Germany

                      #11
                      Originally posted by signal.quest
                      Thanks. I will try that test. Do you think my logic (A) board is OK since it is recognized when laptop is connected to HDMI? Is there any other way to verify it is OK?
                      yes its fine..

                      Comment

                      • signal.quest
                        Senior Member
                        • Oct 2020
                        • 50
                        • United States

                        #12
                        I assume then, the issue is something with the LCD panel? Are there common troubles with this type of panel? Or did I likely damage it from dismantling it to replace the LED backlights? I will try the troubleshooting steps you mentioned. What is the name of the integrated board to the LCD panel called? Is that the TCON or just LCD panel circuit board?

                        Comment

                        • Diah
                          Badcaps Legend
                          • Feb 2013
                          • 6353
                          • Germany

                          #13
                          yours T-CON are interrogated with the Panel buffer boards. to test the panel.. you need
                          disconnect the LVDS cable between main boards and Panel , check on the PSU test point at Cold Area the 12V rail...
                          fed the Panel T-CON boards with 12V direct to fuse FP1 from the rail you found on PSU .. turn on the Tv and check the screen.

                          Notice. be sure the panel buffer boards had connect point to TV chassis
                          Last edited by Diah; 03-22-2024, 02:32 AM.

                          Comment

                          • signal.quest
                            Senior Member
                            • Oct 2020
                            • 50
                            • United States

                            #14
                            If I disconnect the LVDS cable from the main board to the panel then I will have no power connection to the panel - is that correct?
                            I only have 1 cable that connects to the panel. I have previously used my meter and found 12V on the panel when the cable was connected. I know the panel board is getting power.

                            Comment

                            • Diah
                              Badcaps Legend
                              • Feb 2013
                              • 6353
                              • Germany

                              #15
                              Originally posted by signal.quest
                              If I disconnect the LVDS cable from the main board to the panel then I will have no power connection to the panel - is that correct?
                              I only have 1 cable that connects to the panel. I have previously used my meter and found 12V on the panel when the cable was connected. I know the panel board is getting power.
                              we know the panel power right now come via LVDS... this why i wrote disconnect the LVDS and power the panel fuse FP1 with 12V direct from the power boards.... this is test for panel.to have color pattern

                              Comment

                              • signal.quest
                                Senior Member
                                • Oct 2020
                                • 50
                                • United States

                                #16
                                Ok, I understand now. I also can use a dedicated variable bench power supply to power the panel. How may amps does it draw?

                                Comment

                                • Diah
                                  Badcaps Legend
                                  • Feb 2013
                                  • 6353
                                  • Germany

                                  #17
                                  Originally posted by signal.quest
                                  Ok, I understand now. I also can use a dedicated variable bench power supply to power the panel. How may amps does it draw?
                                  wrong... you don't need any external.... we need to use the TV power supply 12V,,, then when you power on the set the LED BL will come on so you can see the panel clearly if there are issue.

                                  Comment

                                  • signal.quest
                                    Senior Member
                                    • Oct 2020
                                    • 50
                                    • United States

                                    #18
                                    The power supply from the TV only outputs 5V, 16V and 24V. The logic board provides 12V. Not sure how I can provide the 12V easily without another supply? Can I just power the backlight with the TV supply and the LCD with a dedicated bench supply?

                                    Comment

                                    • Diah
                                      Badcaps Legend
                                      • Feb 2013
                                      • 6353
                                      • Germany

                                      #19
                                      Originally posted by signal.quest
                                      The power supply from the TV only outputs 5V, 16V and 24V. The logic board provides 12V. Not sure how I can provide the 12V easily without another supply? Can I just power the backlight with the TV supply and the LCD with a dedicated bench supply?
                                      take the 12V from LVDS socket on main boards and connect it to the fuse FP1

                                      Comment

                                      • signal.quest
                                        Senior Member
                                        • Oct 2020
                                        • 50
                                        • United States

                                        #20
                                        I did the following tests:
                                        1. I disconnected both yellow highlighted connections in the picture you sent. This created a white screen on the disconnected side and colored lines in the center. Please see picture.
                                        2. I tried to disconnect just 1 of the yellow connection cables. This made a black screen on both sides, but the colored lines in the center.
                                        3. I checked the panel circuit for shorts on the capacitors but did not find any.
                                        4. I checked the panel board and found 12V, 3.3V, and 24V at different sections. I did not check all possible points. Please let me know specifically what is important to check?
                                        5. I used tape to block all lines on LVDS cable except the 12V line to provide power to the panel. I checked the board to ensure it had voltages, but the panel stayed black.

                                        Please tell me what to check for next. Thank you. I greatly appreciate it.

                                        Comment

                                        Related Topics

                                        Collapse

                                        • JSBJSB
                                          Panasonic OLED TX-65GZ950E no image
                                          by JSBJSB
                                          Hello everyone,

                                          so I have this problem with this OLED that had a LED blinking issue at first.
                                          It was blinking twice so it means according to similar service manuals (I cannot find the proper one) EVDD 24V SOS, Panel or TCON Fault.
                                          Also, the connector from PSU to TCON which supplies 24V was burned (changed it) and saw threads about this topic but didn't relate completely to mine.

                                          First thing was to tape the signal ERRORDETECTION so it would try to initialize. And it didn't so I unplugged the panel from TCON.
                                          Then it started up and went to green light...
                                          05-14-2025, 02:39 PM
                                        • Document Archive
                                          HP Elite Slice G2 + Image Load & Asset Tag Elite Slice i5-7500T Specification for Upgrade or Repair
                                          by Document Archive
                                          This specification for the HP Elite Slice G2 + Image Load & Asset Tag can be useful for upgrading or repairing a desktop PC that is not working. As a community we are working through our specifications to add valuable data like the Elite Slice G2 + Image Load & Asset Tag boardview and Elite Slice G2 + Image Load & Asset Tag schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please...
                                          09-12-2024, 02:20 PM
                                        • Pipolups
                                          Corsair K70 LUX RGB dying LEDs
                                          by Pipolups
                                          Hi there !

                                          I'm having an issue for several weeks with my quite old K70 LUX RGB keyboard. I haven't used it for few months, and once I setup up again my desktop computer, I got several dead LEDs on that keyboard. I tried the Corsair troubleshooting thing (disabling options in iCUE, ...) but nothing changed so I conclude that for some reason some LEDs went in retirement...😅
                                          Decision taken to change these LEDs as I have access to desoldering iron and binocular magnifier, I wrote a ticket to tech support, hopping to obtain the LEDs reference and... They refused to tell me 🙄...
                                          10-08-2024, 11:58 AM
                                        • Document Archive
                                          HP ProBook 450 G6 + Image Load, Asset Tag & Testntag Notebook 400 Specification for Upgrade or Repair
                                          by Document Archive
                                          This specification for the HP ProBook 450 G6 + Image Load, Asset Tag & Testntag Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the 450 G6 + Image Load, Asset Tag & Testntag boardview and 450 G6 + Image Load, Asset Tag & Testntag schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps...
                                          09-06-2024, 10:56 AM
                                        • Document Archive
                                          HP EliteBook 1050 G1 + Image Load & Asset Tag Notebook 1000 Specification for Upgrade or Repair
                                          by Document Archive
                                          This specification for the HP EliteBook 1050 G1 + Image Load & Asset Tag Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the 1050 G1 + Image Load & Asset Tag boardview and 1050 G1 + Image Load & Asset Tag schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that...
                                          09-06-2024, 10:56 AM
                                        • Loading...
                                        • No more items.
                                        Working...