RCA(Proscan) with two seconds of backlight

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  • Chuper
    Member
    • Sep 2017
    • 36
    • Canada

    #1

    RCA(Proscan) with two seconds of backlight

    Model: RLDED4633A-D
    Main board: TP.MS3393.PC821

    There is 10 led light strips with 6 led on each divided between two connectors/lines, so 30 on each connector/line in series, total of 60 led. 21 of these led were open. I changed all open ones. Now I got backlight for about 2 sec. It measures about 145V on two white connectors for led lines for a second without load and climbs up to 75V and slowly drops with them connected when they all briefly come on. I tried checking all strips separately with a power supply applying 20.4V to each and each read about 200mA on my ammeter.
    Any suggestions on what the next step could be would be greatly appreciated.
    Attached Files
  • CapLeaker
    Leaking Member
    • Dec 2014
    • 7967
    • Canada

    #2
    Re: RCA(Proscan) with two seconds of backlight

    Not sure, but on your last picture is seems to me that some 20 or so LEDs are brighter than the others? The LED backlights are driven in current mode. So if the LED controller sees a mismatch in current on what the LEDs should draw and what they actually do draw, the LED controller senses that there is an error in the circuit or with the LEDs and it will shut itself down. Above that red cap CB325 is a little IC. What is the number on it? Should have something similar like OB3350CP. Pull up the spec sheet and see what happens around the pins. These have OVP, OCP, UVLO etc.
    Something else you could try is to turn the backlights waaaay down to next to nothin and see if they stay on. The problem is that there still could be a bad LED hiding, that works for seconds and measures good, but once it gets hot it fails. That's why when that many LED's (like 20 of them) fail, replace them all...

    Comment

    • Chuper
      Member
      • Sep 2017
      • 36
      • Canada

      #3
      Re: RCA(Proscan) with two seconds of backlight

      On some of the strips I replaced just one of them and on some as many as four but testing them individually they all lid up evenly and draw same current. That little IC is AS358M.
      "Something else you could try is to turn the backlights waaaay down to next to nothin and see if they stay on." - maybe not exactly smart question but how do I do this?
      Thank you CapLeaker for you help

      Comment

      • CapLeaker
        Leaking Member
        • Dec 2014
        • 7967
        • Canada

        #4
        Re: RCA(Proscan) with two seconds of backlight

        Well... that's the wrong IC... that would be a dual op amp. I am looking for the backlight PWM.
        You have to turn the backlight down, in the menu settings / picture of the TV. Problem is you have no backlight, so you may have to shine a strong flashlight into the screen.

        "It measures about 145V on two white connectors for led lines for a second without load and climbs up to 75V and slowly drops with them connected when they all briefly come on."
        Could you explain that a little better? We want the exact voltages from each string with the backlights connected.

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: RCA(Proscan) with two seconds of backlight

          We need the Voltage readings of the other two pins also, we know that 2 of the 4 pins are for the LED+ for feeding the Anode of each LED string, we now need the Voltage on the return pins to see what you have, you will have to leave the black probe on the chassis and read probe on the pin then turn on the TV while watching the meter to see what Voltage get, then turn off the TV and move the probe to another pin of the connector and repeat the same procedure, all this is done with EVERYTHING connected.
          When there is no load the Voltage went up to 145V and then it goes into protection shutdown due to no LED's connected so the Voltage drops back down to 75V.
          30 LEDs per string so the Vf of the LED string will be about 90V + Vdrops of about 20V on the PWM controlLed MOSFET, so the output Voltage at the LED connector with working LED connected should be around 110VDC or so.
          Last edited by budm; 11-19-2017, 07:24 PM.
          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

          • Chuper
            Member
            • Sep 2017
            • 36
            • Canada

            #6
            Re: RCA(Proscan) with two seconds of backlight

            So I went to check voltages on LED- (cathode) against chassis. I don't believe in magic but it does work now. Here are voltage readings after TV powers on:
            Connector 1: LED- 0.842Vdc; LED+ 99.7Vdc
            Connector 2: LED- 0.885Vdc; LED+ 99.7Vdc
            So the question is what did happen that it works now after a day of rest?
            Attached Files
            Last edited by Chuper; 11-19-2017, 08:44 PM.

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA

              #7
              Re: RCA(Proscan) with two seconds of backlight

              We cannot tell because we did have all the Voltage readings of all the pins with LED connector in place when you were having problem.
              But make sure to turn down the backlights level (not Brightness)to as low as you can
              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

              • Chuper
                Member
                • Sep 2017
                • 36
                • Canada

                #8
                Re: RCA(Proscan) with two seconds of backlight

                budm are you referring to a setting in a TV menu?

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #9
                  Re: RCA(Proscan) with two seconds of backlight

                  It should be in one of the user on screen setup page.
                  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

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: RCA(Proscan) with two seconds of backlight


                    It does not look like it has one, so you may have to try 'Picture Mode' to see if one of the setting will reduce the backlights level or not, otherwise you can expect the LEDs to fail again since they drive them at max rating.
                    Last edited by budm; 11-19-2017, 10:33 PM.
                    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

                    • Chuper
                      Member
                      • Sep 2017
                      • 36
                      • Canada

                      #11
                      Re: RCA(Proscan) with two seconds of backlight

                      I did go through the menu and looks like there is no way to lower backlight level. Thank you budm for the manual. I guess this thread came to it's end.
                      P.S. amazingly helpful forum you got here guys!

                      Comment

                      • CapLeaker
                        Leaking Member
                        • Dec 2014
                        • 7967
                        • Canada

                        #12
                        Re: RCA(Proscan) with two seconds of backlight

                        That is correct, there are some RCA models that one can't adjust the backlight level. I've ran into this once before a few years ago. I've just remembered because you said it. Why things are working now, I could be still a faulty LED, could be a dirty or bad connection somewhere, a cold solder joint, something along that line. I am glad you got it working for now.

                        Comment

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