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Digihome (Vestel) LED Backlighting Problem

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    #41
    Re: Digihome (Vestel) LED Backlighting Problem

    Originally posted by CapLeaker View Post
    LED's breaking down?
    I've been able to test each of the LEDs by applying 7.2V DC across two bulbs at a time (voltage drop 3.6V across each bulb). 3 individual LEDs aren't working but the rest seem to be ok.

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      #42
      Re: Digihome (Vestel) LED Backlighting Problem

      Originally posted by CapLeaker View Post
      What is the condensed version story of this tv?
      TV failed last week. Switch on, fine, but screen goes blank after a couple of minutes. Restarting the TV fixes the problem but it keeps recurring.

      Sometimes the left half of the screen only goes dark and the right half stays bright, before the whole thing fails.

      Dismantled TV, done lots of checking of LED bulbs, voltages at various different points, etc. but I'm struggling to make sense of it. Don't think LEDs are all faulty on one side of the screen (3 individual bulbs have failed on the other side of the screen but it doesn't stop the others working). Can't find any broken connections - everything seems intact.
      Attached Files
      Last edited by bigalxyz; 08-21-2016, 11:41 AM.

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        #43
        Re: Digihome (Vestel) LED Backlighting Problem

        In that pic, one led is out on the very top left.

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          #44
          Re: Digihome (Vestel) LED Backlighting Problem

          Correct - the other two faulty bulbs are in the middle row (with the black arrows next to them). Not apparent from the photo though - tested with a 7.2V battery

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            #45
            Re: Digihome (Vestel) LED Backlighting Problem

            The two and a half strips that work - voltage drop across each bulb is 2.4 - 2.5V, nice steady bright light.

            The two and a half strips that don't work - voltage drop across each bulb is ALSO 2.4 - 2.5V, but they just barely light up. Not only that, but they stay in their just barely lit up state when I put the TV in standby mode!

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              #46
              Re: Digihome (Vestel) LED Backlighting Problem

              Those LEDs are set like Christmas lights. Did you follow Reeceys suggestion about bridging? LED's can fail different ways. Open, short, or fail when they get hot. Maybe there is a bad solder joint somewhere, who knows. You may swap some strips around if it is possible. Maybe a connector could be lose or bad connection etc.
              Last edited by CapLeaker; 08-21-2016, 01:37 PM.

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                #47
                Re: Digihome (Vestel) LED Backlighting Problem

                Originally posted by CapLeaker View Post
                Those LEDs are set like Christmas lights. Did you follow Reeceys suggestion about bridging? LED's can fail different ways. Open, short, or fail when they get hot. Maybe there is a bad solder joint somewhere, who knows. You may swap some strips around if it is possible. Maybe a connector could be lose or bad connection etc.
                I haven't bridged the connectors to the LED strips, no. My test meter tells me all the voltage coming from the PSU is getting through to the strips as it should - have checked carefully - so I can't see how this would help. Am I missing something?

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                  #48
                  Re: Digihome (Vestel) LED Backlighting Problem

                  Originally posted by bigalxyz View Post
                  I haven't bridged the connectors to the LED strips, no. My test meter tells me all the voltage coming from the PSU is getting through to the strips as it should - have checked carefully - so I can't see how this would help. Am I missing something?
                  yours way to test LED wrong. sorry.. as CL wrote before LED are currents not voltage. this mean, each LED had one Ziner Diode bulit in at opposite way, so you need to turn off the TV and each LED with yours test metter als Diode make the measurement,, each LED give you measure in Diode way resistances less than 50 its bad and drain currents. shortet mean will be zero and DMM will peep on

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                    #49
                    Re: Digihome (Vestel) LED Backlighting Problem

                    Originally posted by Diah View Post
                    yours way to test LED wrong. sorry.. as CL wrote before LED are currents not voltage. this mean, each LED had one Ziner Diode bulit in at opposite way, so you need to turn off the TV and each LED with yours test metter als Diode make the measurement,, each LED give you measure in Diode way resistances less than 50 its bad and drain currents. shortet mean will be zero and DMM will peep on
                    Thank you. I understand. I did try using my multimeter in diode mode on Thursday but I can't remember what it told me! (although I do remember that it made the LEDs light up a tiny amount) I'll try it again tomorrow...

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                      #50
                      Re: Digihome (Vestel) LED Backlighting Problem

                      don't give attention on if they light up or not in this stage.. just focus on the Diode way.. you have one line good, take the measurement of one LED as references to compare with other dimm or off one.

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                        #51
                        Re: Digihome (Vestel) LED Backlighting Problem

                        I've quickly tested now. In diode modes the good LEDs (the ones that I've seen light up with my 7.2V battery) show numbers of about 1050. However two of the bad ones give numbers of 100 or 200. And one of the other LEDs shows "1" on the screen which I think means an open circuit, so presumably infinite resistance, no complete circuit and no current flowing?

                        The bit I don't understand is that I got these numbers by reversing the leads on the multimeter, so that the "ground" lead on the meter (black) was connected to the + side of the LED, and the "live" lead on the meter (red) was connected to the - side of the LED. I hadn't expected this. But I don't get any numbers if I swap the leads around, just "1" (open circuit) every time.
                        Last edited by bigalxyz; 08-21-2016, 02:25 PM.

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                          #52
                          Re: Digihome (Vestel) LED Backlighting Problem

                          I worry that I've shagged something elsewhere because the return voltage on one of the leads from the PSU has dropped to zero. But one problem at a time...

                          Comment

                            #53
                            Re: Digihome (Vestel) LED Backlighting Problem

                            you use analogue test meter ?

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                              #54
                              Re: Digihome (Vestel) LED Backlighting Problem

                              Im out.
                              Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

                              https://www.facebook.com/Telford-Tel...7894576335359/

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                                #55
                                Re: Digihome (Vestel) LED Backlighting Problem

                                the diode test should be done not via the black or red or brown... you should scratch the line of each LED to test direct on the LED self.

                                mean the diode test of led should not as groupr or double.. must be each led alone.
                                Last edited by Diah; 08-21-2016, 02:41 PM.

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                                  #56
                                  Re: Digihome (Vestel) LED Backlighting Problem

                                  Originally posted by Diah View Post
                                  you use analogue test meter ?
                                  No, it's digital. Photo below...
                                  Attached Files

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                                    #57
                                    Re: Digihome (Vestel) LED Backlighting Problem

                                    Originally posted by Diah View Post
                                    the diode test should be done not via the black or red or brown... you should scratch the line of each LED to test direct on the LED self.
                                    Yes, that's what I did - I scratched through the surface of the strips before and after each LED so that there is a little bit of copper underneath.

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                                      #58
                                      Re: Digihome (Vestel) LED Backlighting Problem

                                      1050 are so much from my experiences it should be round 780

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                                        #59
                                        Re: Digihome (Vestel) LED Backlighting Problem

                                        check all the working one did one give you less than 1050

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                                          #60
                                          Re: Digihome (Vestel) LED Backlighting Problem

                                          Originally posted by Diah View Post
                                          check all the working one did one give you less than 1050
                                          No, very consistent for the good LEDs, all very close to 1050. So I have to assume that's the "correct" number.

                                          As I said, I saw 100 from one of the dead LEDs, 200 from another one, and open circuit (infinite resistance) from another.

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