Hitachi 50HYT62U Backlight brief flash

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  • mutts
    Member
    • Jun 2018
    • 11
    • United Kingdom
    #1

    Hitachi 50HYT62U Backlight brief flash

    Hi repairers I have a confusing one (for me).

    A friend has asked me to repair his 2 year old tv, is this a led driver fault?...
    Tv boots normally but no backlights other than a very brief flash. Tested with GJ2C tester all leds come on at 186v. During boot get 162v at connector, brief flash from backlight as voltage slowly rises to 236v, if the set is left on this drops to around 60v over the next 5 minutes.

    All diodes test ok, all capacity and esr of caps is good, lcd panel is unmarked and menu etc can be viewed with a flashlight. Psu is a Vestel 17IPS20, set has done 12.5k hours.

    I'm thinking that regardless of having 2.6v at each of the backlights 63 leds during boot the current is not enough.. and then the climbing voltage?? it's got me.

    If anyone more knowledgeable has any ideas I would be most grateful.
    Thanks
    Tags: None
    • Andrew F. Ali
      Badcaps Legend
      • Jan 2014
      • 2450
      • Trinidad & Tobago
      #2
      Re: Hitachi 50HYT62U Backlight brief flash

      I still suspect bad backlight LEDs. From what I gather the LED Driver seems to be working.

        Comment

        • mutts
          Member
          • Jun 2018
          • 11
          • United Kingdom
          #3
          Re: Hitachi 50HYT62U Backlight brief flash

          Yes that would make sense. I probably missed one or more when checking with the lcd still attached.
          Many thanks.

            Comment

            • zomi
              Badcaps Veteran
              • Nov 2011
              • 505
              #4
              Re: Hitachi 50HYT62U Backlight brief flash

              https://tinyurl.com/yc4accjm

              these should be the strips for yours

                Comment

                • mutts
                  Member
                  • Jun 2018
                  • 11
                  • United Kingdom
                  #5
                  Re: Hitachi 50HYT62U Backlight brief flash

                  Thanks zomi, perfect.

                    Comment

                    • ducky29
                      Badcaps Veteran
                      • Dec 2015
                      • 370
                      • Europe
                      #6
                      Re: Hitachi 50HYT62U Backlight brief flash

                      Did you strip the whole screen down and check all the led strips?
                      Or just test them from the connector that connects with the power supply?

                        Comment

                        • mutts
                          Member
                          • Jun 2018
                          • 11
                          • United Kingdom
                          #7
                          Re: Hitachi 50HYT62U Backlight brief flash

                          They were just tested from the connector, stripping a large panel apart wasn't an option at friends house.

                            Comment

                            • ducky29
                              Badcaps Veteran
                              • Dec 2015
                              • 370
                              • Europe
                              #8
                              Re: Hitachi 50HYT62U Backlight brief flash

                              Originally posted by mutts
                              They were just tested from the connector, stripping a large panel apart wasn't an option at friends house.
                              Well sometimes only few of the leds lit up and give you the illusion that the whole strip works.

                                Comment

                                • budwich
                                  Badcaps Legend
                                  • Jul 2015
                                  • 3097
                                  • Canada
                                  #9
                                  Re: Hitachi 50HYT62U Backlight brief flash

                                  did you try unplugging the strings and then checking the initial open circuit voltage to see where it gets to?

                                    Comment

                                    • mutts
                                      Member
                                      • Jun 2018
                                      • 11
                                      • United Kingdom
                                      #10
                                      Re: Hitachi 50HYT62U Backlight brief flash

                                      Yes, iirc it was around 80v.

                                        Comment

                                        • GAStuntman
                                          Senior Member
                                          • Dec 2017
                                          • 65
                                          • United States
                                          #11
                                          Re: Hitachi 50HYT62U Backlight brief flash

                                          Did you figure out the issue? I’m having the same problem with my tv. I opened it up & tested the LEDs & they all worked using the LED tester. I reassemble the tv & once the power button is pressed the LEDs flash and go back out. I have replaced the power supply board & the LED driver board.

                                            Comment

                                            • budm
                                              Badcaps Legend
                                              • Feb 2010
                                              • 40746
                                              • USA
                                              #12
                                              Re: Hitachi 50HYT62U Backlight brief flash

                                              Originally posted by GAStuntman
                                              Did you figure out the issue? I'm having the same problem with my tv. I opened it up & tested the LEDs & they all worked using the LED tester. I reassemble the tv & once the power button is pressed the LEDs flash and go back out. I have replaced the power supply board & the LED driver board.
                                              Did you use the LED tester to test the whole LED string from the LED connector side? What Voltage does it show on the LED tester?
                                              Never stop learning
                                              Basic LCD TV and Monitor troubleshooting guides.
                                              http://www.badcaps.net/forum/showthr...956#post305956

                                              Voltage Regulator (LDO) testing:
                                              http://www.badcaps.net/forum/showthr...999#post300999

                                              Inverter testing using old CFL:
                                              http://www.badcaps.net/forum/showthr...er+testing+cfl

                                              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                              http://s807.photobucket.com/user/budm/library/

                                              TV Factory reset codes listing:
                                              http://www.badcaps.net/forum/showthread.php?t=24809

                                                Comment

                                                • GAStuntman
                                                  Senior Member
                                                  • Dec 2017
                                                  • 65
                                                  • United States
                                                  #13
                                                  Re: Hitachi 50HYT62U Backlight brief flash

                                                  I tested the LEDs all the voltage was good & all the LEDs did light up with the tester. I don’t remember the exact voltage reading on the LEDs. Normally with LEDs you can shine a flashlight into the screen and see the image. In my case that didn’t work. Like I stated before I have already taken the tv apart and tested the LEDs and they all worked. I’m thinking there maybe a shortage somewhere or something else is causing the tv to shut off the LEDs as a safety precaution.

                                                    Comment

                                                    • budm
                                                      Badcaps Legend
                                                      • Feb 2010
                                                      • 40746
                                                      • USA
                                                      #14
                                                      Re: Hitachi 50HYT62U Backlight brief flash

                                                      LED tester only puts out 30mA compared to about 300 ~ 400mA when driven by the TV LED driver circuit. I do have LED tester that I use as a guide but not for 100% verification of the condition of the LED's. Bad LED will fail when driven at high current.
                                                      You can disconnect the LED connector from the power supply board and use your tester to light up the LED string and verify for sure if you do not have any image on the screen or not, if not then check the fuse on the T-CON board and see if you do have 12VDC at both ends of the fuse with ref. to chassis GND.
                                                      Last edited by budm; 01-18-2019, 11:39 AM.
                                                      Never stop learning
                                                      Basic LCD TV and Monitor troubleshooting guides.
                                                      http://www.badcaps.net/forum/showthr...956#post305956

                                                      Voltage Regulator (LDO) testing:
                                                      http://www.badcaps.net/forum/showthr...999#post300999

                                                      Inverter testing using old CFL:
                                                      http://www.badcaps.net/forum/showthr...er+testing+cfl

                                                      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                                      http://s807.photobucket.com/user/budm/library/

                                                      TV Factory reset codes listing:
                                                      http://www.badcaps.net/forum/showthread.php?t=24809

                                                        Comment

                                                        • GAStuntman
                                                          Senior Member
                                                          • Dec 2017
                                                          • 65
                                                          • United States
                                                          #15
                                                          Re: Hitachi 50HYT62U Backlight brief flash

                                                          Thanks, I took the tv back apart & found one burnt LED. Replacing the bad LED fixed the issue.

                                                            Comment

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