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50UH5500 No picture/sound

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    50UH5500 No picture/sound

    So I picked up this 50UH5500 the other day.

    When I power it up, the main board gets power for brief second, the backlights flash and then power shuts down to the Backlights and Main.

    Testing the PSU-
    With the Power plugged in
    Power
    pin 1- STB - 0 V
    pin 2,3 - 0 V
    Pin 4,5,6,7,8 - get 10.22 V
    pins 9,10,11,12 - 0 Volts

    where the LED plug is.
    pins 1,2,3 - 88-89 Volts
    pins 4,6 give 27-28 volts.
    pin 5 - 0 Volts

    Based on the LED pin voltages, I'm assuming i have a bad LED. However the weird thing that gets me is the STB being 0 V. I always thought they were supposed to be about 3.5 V.

    Reading at ShopJimmy...that these TV's also really had a tendency to have LED Failure as well.
    Attached Files

    #2
    Re: 50UH5500 No picture/sound

    First check the power board by itself, so get a car light bulb or a ceiling headlight with 12v 50w and put it on the 13v/0v outputs, if it light up well and steady P.B. is ok. It's impossible that mainboard did get power for some seconds 'cause PSU is always on. The STB=standby signal is only from m.b. to p.b to switch on the PFC. So i guess you have a mainboard problem. It is almost sure because PSU have no error signal that can switch off some tensions on the m.b. in a standby state. You can have a standby software messed up or a short circuit on a regulation stage or a mpu or cpu. etc..

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      #3
      Re: 50UH5500 No picture/sound

      Originally posted by Davi.p View Post
      First check the power board by itself, so get a car light bulb or a ceiling headlight with 12v 50w and put it on the 13v/0v outputs, if it light up well and steady P.B. is ok.
      ok I can get a car light bulb, but not sure what you mean by put it on the 13v/0v outputs - the outputs on the power connector and just physically place it against the pins? Or should I purchase a few connector wires or such?

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        #4
        Re: 50UH5500 No picture/sound

        Pin 1 STB = PS-ON
        Pin 11 ENA = BL-ON
        Pin 12 ADJ = Backlights dimmings

        So the main board is not sending the control signals to the power supply board.
        Last edited by budm; 02-09-2020, 12:44 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


          #5
          Re: 50UH5500 No picture/sound

          I mean only that a bulb need two poles connected, 13v and 0v.. Check well the tension under load because that 10v is not OK..
          sorry i change my diagnosis, i haven't noticed well the 10v, i thought you had low bat on tester, but seems not ok the PSU that outputs a little current then goes into protection. If the test fails post a picture of the underside of the psu. I correct myself, the PFC can't be activated by STB 'cause there's 1 only opto. I don't figure out to understand what STB does..
          Last edited by Davi.p; 02-09-2020, 03:04 AM.

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            #6
            Re: 50UH5500 No picture/sound

            Turned out that it was a bad LED strip.

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