42LG50 no backlight

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • torpex505
    Member
    • Sep 2010
    • 41

    #41
    Re: 42LG50 no backlight

    ok, I disconnected the ribbon that connected the inverter to the T-con board, there was still no light after powering on. I reconnected that ribbon cable and disconnected the harness that connected the T-con board from the I/O board, still nothing. I then left the harness disconnected and disconnected the ribbon cable from the main inverter again, and still no light.

    Comment

    • tommyjaxx
      New Member
      • Nov 2010
      • 1

      #42
      Re: 42LG50 no backlight

      Torpex, im going thru the exact same thing......exact same TV same. I have no new info to offer as of yet but I am right there with you, tryingto figure this bugger out.

      Comment

      • torpex505
        Member
        • Sep 2010
        • 41

        #43
        Re: 42LG50 no backlight

        Sorry to hear that you're having the same problems. Let us know what you find out with yours. I've lost patience with mine. I'll pull it back out in a few weeks to start looking at it some more. Good luck.

        Comment

        • dietzcj
          Senior Member
          • Mar 2011
          • 114

          #44
          Re: 42LG50 no backlight

          Torpex and tommyjaxx ,
          I have an LG 42lg50-ua as well that I am troubleshooting.
          When I plug it in, I get no flash on the backlights, but just the red flashing light at the power button.
          I have also Unplugged both inverters, Same result (Red light flashing).
          I have unplugged the T-con board, Same result (Red light flashing)
          Unplugged both inverters, and T-con board, same result (Red light flashing).
          There are no bad capacitors (Bulging or leaking). I have resoldered nearly all joints.

          I have no problem ordering a new power board from ebay, but I just want to make sure I have isolated the part where the problem exists.

          I think we can all solve this together.

          Comment

          • torpex505
            Member
            • Sep 2010
            • 41

            #45
            Re: 42LG50 no backlight

            Originally posted by dietzcj
            Torpex and tommyjaxx ,
            I have an LG 42lg50-ua as well that I am troubleshooting.
            When I plug it in, I get no flash on the backlights, but just the red flashing light at the power button.
            I have also Unplugged both inverters, Same result (Red light flashing).
            I have unplugged the T-con board, Same result (Red light flashing)
            Unplugged both inverters, and T-con board, same result (Red light flashing).
            There are no bad capacitors (Bulging or leaking). I have resoldered nearly all joints.

            I have no problem ordering a new power board from ebay, but I just want to make sure I have isolated the part where the problem exists.

            I think we can all solve this together.

            Hi dietzcj,

            I'm not too sure about this, but I think the red light would be an indication of a power problem(or possibly one of the inverters). The light on mine is blue when on and red when off (if I remember correctly.) Which I believe indicates that the TV thinks it's functioning correctly.

            The backlight does not flicker on mine either, they just don't come on at all. Have you put a flashlight to the screen to see if you have picture?

            Comment

            • dietzcj
              Senior Member
              • Mar 2011
              • 114

              #46
              Re: 42LG50 no backlight

              As soon as I plug in the power cord the red light starts flashing.
              I have not done that flash light thing so I will try that when I get home.

              Comment

              • dietzcj
                Senior Member
                • Mar 2011
                • 114

                #47
                Re: 42LG50 no backlight

                Would it seem logical that the problem exists on the power board if I do not have either converter plugged in and I get the same result ?

                Comment

                • dietzcj
                  Senior Member
                  • Mar 2011
                  • 114

                  #48
                  Re: 42LG50 no backlight

                  If it helps I have the service manual for the LG 42lg50.
                  Attached Files

                  Comment

                  • Dgtech
                    E. Technician
                    • Apr 2009
                    • 1462
                    • Steeler

                    #49
                    Re: 42LG50 no backlight

                    If there is any flashing LED indicators on either of your sets, I'd specify the rate in which they are flashing. Many sets have various meanings for what each flashing code indicates. It will point out your problem sometimes. Posting pictures of the power board and the whole set layout (opened) would help a great deal as well.
                    Last edited by Dgtech; 03-04-2011, 05:29 PM.
                    The strong-minded rise to the challenge of their goals,the weak-minded BECOME HATERS

                    Comment

                    • mbates14
                      Senior Member
                      • May 2005
                      • 169

                      #50
                      Re: 42LG50 no backlight

                      This looks like the same setup as the magnovox inverters I have worked on. in my experience, they either produce no backlight, or maybe a flicker of a backlight before going out.

                      its almost ALWAYS due to a faulty transformer. you MUST pull all transformers, one at a time, and do a resistance check on all windings. keep a chart. youll find a bad one.

                      Comment

                      • dietzcj
                        Senior Member
                        • Mar 2011
                        • 114

                        #51
                        Re: 42LG50 no backlight

                        @torpexx:
                        No pitcure with the flash light test.
                        The red light flashing is a simple 2 second fade on and off

                        Did you read my previous post with the statements where I unplugged both Master and Slave inverters ? I unplugged them both and then connect to power and I get the same result. i did the same with the T-con card.

                        I will post photos once my camera is done charging.

                        Comment

                        • Dgtech
                          E. Technician
                          • Apr 2009
                          • 1462
                          • Steeler

                          #52
                          Re: 42LG50 no backlight

                          Originally posted by dietzcj
                          @torpexx:
                          The red light flashing is a simple 2 second fade on and off
                          Try to find out what this code means. This will give you a clue 99 percent of the time. Look for a service manual. They should tell you what this means and how to fix it.
                          The strong-minded rise to the challenge of their goals,the weak-minded BECOME HATERS

                          Comment

                          • dietzcj
                            Senior Member
                            • Mar 2011
                            • 114

                            #53
                            Re: 42LG50 no backlight

                            here are the pics
                            Attached Files

                            Comment

                            • dietzcj
                              Senior Member
                              • Mar 2011
                              • 114

                              #54
                              Re: 42LG50 no backlight

                              dgtech, I posted the service manual above. I would like to know what that code means, it is not really posted in any service manual or LG support.
                              I have a phone number to an LG service repair tech who should know the answer.
                              Thanks for all the comments.

                              Comment

                              • dietzcj
                                Senior Member
                                • Mar 2011
                                • 114

                                #55
                                Re: 42LG50 no backlight

                                Okay, so I talked with my LG guy in Virginia and he says that the red flashing lights means that the unit is going directly to "Standby" and not even making an effort to power up the inverters.
                                THis is confirmed since I unplugged both inverters in my initial testing.
                                He said that capacitors are usually the cause on these power supply boards (from what they have serviced). I do not see any that are bulging or leaking but that may not always be the case with bad capcitors.
                                I will take each one out and test with my multimeter.
                                Worst case I can just replace them all (9 of them) and see what happens.

                                He definitely thinks it is the power supply though.
                                I will post my finidings here later tonight.

                                Comment

                                • Scenic
                                  o.O
                                  • Sep 2007
                                  • 2640
                                  • Germany

                                  #56
                                  Re: 42LG50 no backlight

                                  the caps look like they're Sam Young -> replace on sight (all of them, except the big 400+V one)

                                  Comment

                                  • dietzcj
                                    Senior Member
                                    • Mar 2011
                                    • 114

                                    #57
                                    Re: 42LG50 no backlight

                                    @Scenic: what do you mean by "Sam Young" ???

                                    Comment

                                    • Scenic
                                      o.O
                                      • Sep 2007
                                      • 2640
                                      • Germany

                                      #58
                                      Re: 42LG50 no backlight

                                      the manufacturer of those crappy capacitors on that PSU board..
                                      http://www.samyoung.co.kr

                                      Comment

                                      • torpex505
                                        Member
                                        • Sep 2010
                                        • 41

                                        #59
                                        Re: 42LG50 no backlight

                                        Sorry, I had a busy weekend moving the ex out. It seems like you're on the right track. I've been looking everywhere for that manual, so thanks for posting it. I'll try to look it over tonight.

                                        Comment

                                        • dietzcj
                                          Senior Member
                                          • Mar 2011
                                          • 114

                                          #60
                                          Re: 42LG50 no backlight

                                          Well, I ended up just buying an entire power supply card from ebay for $30. When I get it and install, I will post results here.

                                          Comment

                                          Related Topics

                                          Collapse

                                          • triplefour
                                            UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt fix!
                                            by triplefour
                                            this tv is throwing me for a loop. do samsung tvs no longer have the backlight self test feature built into the power supply?
                                            i tested the backlight with my LED tester and it lights up both strips. one of them reads 100v and the other reads 63.7v.
                                            unplugged mainboard from power supply but left backlight plugged in, and then plugged psu wall power in. expected to see backlights light up but see nothing.
                                            according to how ive diagnosed in the past, this would almost always be a bad power supply. replacement power supply was cheap like 20$ from ebay. but still i get not even...
                                            09-13-2023, 10:43 PM
                                          • DanPoka
                                            Guide me through repairing a Dell p2210f LCD ccfl backlight monitor
                                            by DanPoka
                                            I bought this p2210f dell monitor to fix. Schematic is the same as p2210.
                                            Behaviour is that monitors comes on but then backlight switches off almost instantly. If I look with flashlight I can still find the "No signal message". So definitely a backlight issue. Trying to advance the issue I proved that the protection circuit is switching off the backlight by shorting out C3 and resistor to disable the INL chip then re enable by removing the short.
                                            This is where it gets interesting. When I disassembled the monitor to solder leads on c3 capacitor I noticed the backlight flickered...
                                            02-15-2025, 05:05 AM
                                          • Comp_Pro
                                            No Backlight Macbook A1990 820-01041
                                            by Comp_Pro
                                            Hello all,

                                            Am trying to figure out this backlight issue with this A1990 Macbook Pro.

                                            Tests performed:

                                            There is no backlight even with a good screen.
                                            Backlight IC is receiving the correct support voltages.
                                            Fuse F8400 ok
                                            Current sense resistor R8400 ok
                                            Backlight IC is receiving 3.3V on enable pin.
                                            Backlight IC receiving voltage from PPBUS_G3H, aprox 12.5V.
                                            Backlight IC receiving 5V from PP5V_G3S
                                            Backlight IC BKLT_SCL and BKLT_SDA both measure 0.545V diode mode to ground
                                            I2C_BKLT_SCL and I2C_BKLT_SDA both measure...
                                            05-06-2024, 10:23 PM
                                          • jimbofz
                                            lg 32LC46 backlight inverter board fault
                                            by jimbofz
                                            Hi this oldie had no backlight .after replacing caps on 24v rail ,
                                            still no b/l this uses inverter type:1315 B1-16A,
                                            im sure ive come across the same inverter in a samsung possibly le32r88bd ?
                                            all t/x in board test ok ,so i fitted 15k and led to pin 4 of oz964gn ic
                                            this allows protect to be temporary overridden.
                                            b/l now comes on
                                            but the left hand side of pic is gradually darker than the right side
                                            i have the cct for the tv
                                            but it does not have inverter cct.
                                            i opened it up to inspect the ccfl tubes
                                            and they dont have any...
                                            12-19-2021, 06:58 AM
                                          • cheebster
                                            iPad Pro 12.9 5th Gen Backlight Issue
                                            by cheebster
                                            Hello, got an iPad Pro A2378 12.9 5th gen with no backlight. Got another test unit without screen, tested the screen, still no backlight with the test unit.
                                            Figured out the backlight on the screen was bad, ordred a new backlight from mobilesentrix, *carefully replaced it* without damaging the lcd, oh well.
                                            Final result, issue is still there, the screen has no back lights. So i'm back to square one, with 3 hours less and 100$ out, issue still on the screen.
                                            The panel is still ok, i can see the apple in the middle of the screen when it kicks in, just no backlight.
                                            Anyone...
                                            05-20-2025, 09:17 AM
                                          • Loading...
                                          • No more items.
                                          Working...