Panasonic TC-P50G25 SC board TNPA5081AF shorting again after repair

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  • Yanleb
    Senior Member
    • May 2017
    • 101
    • Canada

    #1

    Panasonic TC-P50G25 SC board TNPA5081AF shorting again after repair

    Hi all,

    After repairing my TNPA5081AF, it shorts out immediately after powering it.

    I traced down the problem to the SOT23-5 Inverter IC773 (marked HA on its case, and IC16773 on the schematic). The chip receives a supply voltage of 5 volts but it receives 16 volts on its input. This is what I measure on the board, and this is also what I see on the schematic.

    I think that I found the data sheet of the IC773 chip. It should be a TC7SH14F. Its max input voltage is 7 volts. This is not a surprise that the chip will short out when it receives 16 volts on its input.

    Did you already had problems with this chip? What would be the correct replacement?

    Thanks.
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  • lotas
    Badcaps Legend
    • Jan 2016
    • 4568
    • Russia

    #2
    Yes, everything is correct, this is C0JBAB000715 IC(16)773 "TC7SH14F"
    Attached Files

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    • Yanleb
      Senior Member
      • May 2017
      • 101
      • Canada

      #3
      Thank you for confirming the part number. But can you explain why it is shorting out immediately? I just don't understand why there's a transistor to pull the input to 16V_F while the input is only rated at 7 volts.

      The schematic matches the board. And effectively I measure 5 volts at pin 5 VCC and 16 volts at pin 2 IN_A. Does it mean that this is a design flaw? Or that Q16702 is not supposed to be turned on?

      Maybe I'm wrong to assume that 16V_F is 16 volts in reference to VAD. Can someone confirm?

      Another question, can someone explain me why the base of Q16701 is connected to ground?

      Comment

      • Biruslapio
        Badcaps Veteran
        • Nov 2013
        • 552
        • Brasil

        #4
        any _F = floating ground, which is a ground specific to plasma sustain voltages in the tv, it's the same as probing the screws that go into between SC and buffer boards.

        Comment

        • kasfamily
          Badcaps Veteran
          • Aug 2014
          • 765
          • Russia

          #5
          https://www.badcaps.net/forum/troubl...-rebuild/page8

          ​

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