T3D 21 - zener diode?

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  • jm1234
    Senior Member
    • Jan 2024
    • 59
    • Slovakia
    #1

    T3D 21 - zener diode?

    Hi,
    I'm looking at the power source module of my Panasonic plasma TV TX-P42ST50. The TV goes into suspended state almost immediately and keeps flashing 6 times.
    That zener diode is marked on the board with the diode sign (D204), that much I know. It seems to be open completely in both directions and its legs seem dark, as if it suffered some heat.
    I'm having trouble finding a replacement. Does 21 stand for 21V?
    The only other clue I have it is connected across 2 of the legs of a transformer (primary side).
    Any idea how to find a replacement?
    Thanks
    Click image for larger version Name: Screenshot 2024-04-14 203936.png Views: 0 Size: 212.8 KB ID: 3252836
    Tags: None
    • jm1234
      Senior Member
      • Jan 2024
      • 59
      • Slovakia
      #2
      I went ahead, bought 22V 5W zener, replaced it and the TV doesn't even try to power on now. I removed it again and we're back to what it was (6 led flushes and turns off). So burnt zener (or none) seems to work better.

        Comment

        • CapLeaker
          Leaking Member
          • Dec 2014
          • 7971
          • Canada
          #3
          Not seeing any markings of the diode, I think it is something like a 1.5KE200CA which is a BIdirectional TVS protection diode. It being open on both ends, this is correct and not a failure. Basically 2 diodes opposing each other in one package.
          If that diode sits across the primary it’s not 21V. Hard to tell with no pictures.
          Last edited by CapLeaker; 04-17-2024, 04:48 AM.

            Comment

            • jm1234
              Senior Member
              • Jan 2024
              • 59
              • Slovakia
              #4
              Oh that would make sense, learning something new every day. It seems I got to know about components just enough to cause problems :-).
              Anyhow, the markings are in the topic name: T3D 21 (with the digit 1 underscored if that makes any difference). The original diode has dark discoloration on its legs, as if it suffered some heat.
              I measured the voltage between those 2 transformer legs and my meter shows some 800~900V AC, but it only has 750V range, so not sure how reliable that is (I should've measure that before I ordered that zener diode). That value doesn't make much sense to me, as I tried to follow the circuit visually and it seems the transformer is fed almost directly from a bridge rectifier that produces 330V DC (I measured). All in all, more questions than answers.
              Still it seems that TVS diode is not the culprit here, so I might as well put it back there.
              Thanks

                Comment

                • CapLeaker
                  Leaking Member
                  • Dec 2014
                  • 7971
                  • Canada
                  #5
                  ??? Huh? 800 to 900VAC? I don’t think so. Not sure what’s going on with your DMM.

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