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Bad Video on a cheap MASTER LCD TV,Motherboard model: tp.s506.pb801

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    Bad Video on a cheap MASTER LCD TV,Motherboard model: tp.s506.pb801

    Hi all, I have a cheap LCD with a cheapo brand name "MASTER", it's one of those sets with a single PCB (Motherboard model: tp.s506.pb801) that handles everything. It powers up fine but shows signs that usually indicate a TCON problem (see images) however there is no TCON to troubleshoot, where should I start troubleshooting, on the mainboard? or the LCD's PCB? I tried tapping the thin LCD PCB while it was running and only got a change in video when I tapped a certain IC on the board (see picture below, IC circled in red) and the screen went dark and came back but now it was white instead of having the weird green haze seen in the first picture when I removed my hand, I tried probing the IC with my multimeter and when probing the bottom right pin (from the orientation of the image) to see if there is any voltage on it the whole screen went darker and came back to normal when I stopped probing. I have no clue of what I'm doing really as I've never encountered video issues on a TV, does this indicate anything about the state of the IC? Any ideas? Thanks
    Attached Files

    #2
    Re: Bad Video on a cheap LCD TV

    Your t-con is on the panel board. You have test points vgh, vgl, vcom and others you can check.
    I assume no responsibility for any stupid suggestions I might post.

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      #3
      Re: Bad Video on a cheap LCD TV

      Thanks for the help, I checked the test points and all seem to be operating fine:

      VIN : 12V
      VDDA : 12V
      VCOM : 5V
      VGL : -6V
      VGH : 30V
      V33_S : 3.3V
      V33_T : 3.3V
      V33_E : 3.3V

      any ideas on how to proceed?

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        #4
        Re: Bad Video on a cheap LCD TV

        Check voltage on L502 while tapping and make sure voltage is steady.
        I assume no responsibility for any stupid suggestions I might post.

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          #5
          Re: Bad Video on a cheap LCD TV

          Voltage on L502 drops from 3.3v to 1.4v when I touch it, doesn't seem like it's supposed to do that.. Could it be an issue with the power 3.3v power rail?

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            #6
            Re: Bad Video on a cheap LCD TV

            Found something.. the 3v3 rail is shorted to GND through 10 ohms, I disconnected the Main board to make sure the short wasn't coming from there, should I try to inject voltage and see what gets hot? I'm surprised that It shows as 3.3v on my meter even tough it has a 10ohm short on it

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              #7
              Re: Bad Video on a cheap LCD TV

              Does picture change with voltage. Do you get good picture or lines?
              I assume no responsibility for any stupid suggestions I might post.

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                #8
                Re: Bad Video on a cheap LCD TV

                When the voltage drops to 1.4v, i still get bad picture but dimmer

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                  #9
                  Re: Bad Video on a cheap LCD TV

                  Update: Injected voltage at the 3v3 rail and felt the NT71710MFG-000 IC get warm with 2Amps going in, I removed the chip and now resistance went from 10 ohms to 15.5kohm and the couple of resistors around the chip which I previously found to be shorted are fine now, no more shorts. Seems like the IC is the cause of the issues, I'll order a replacement and see what happens...

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