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Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

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    Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

    If the 16v is staying up and the 68Ω got warm, I would say the standby circuit is working. and the primary side and feedback/regulation is all ok.
    Adding a load to the 6v line is the only way to check if it is working and able to supply current. About a 15Ω resistor should draw around 500ma, and the circuit should be able to supply that without a problem.
    Reconnect ic501, does the vin stay up?

    These power supplies were very reliable and the original problem was likely not on the power supply. I would check all the work you have done on it so far.
    Last edited by R_J; 12-08-2021, 06:21 PM.


      Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

      All the latests tests I had done with the IC501 fully connected so since you mentioned reconnecting it, I took it out in the first place.
      And this time I really took it our completely. I think I should have done that earlier because all my attempts to measure around it by cutting lines on the board just messed it up. Still to a point where all the lines are okay, it just doesnt look as good.

      So without the IC501 I get 9.8V where Vin would be.

      I realized I made a mistake yesterday by putting the Load resistor in Series with my Voltmeter. Of course it has to be in parallel

      So now when I put the 15Ω load between Vin and Gnd of IC501 the voltage drops significantly to 3.5V. With the 35Ω it drops to 4.2V.
      So I thought there was a load dependant voltage drop on the second supply.

      Knowing my stupid mistake with the measurement I wanted to retest the 15V line with a load in parallel, but found it wasnt there anymore. And now the 9.8V on Vin are gone too.
      To my understanding of the Block diagram that is because without IC501 RL100 wont switch.
      I guess when I measured earlier it was still closed on the charge of some cap and I still dont know if the voltage really drops.

      I need to do more testing
      Last edited by Ierwin; 12-09-2021, 01:53 AM.


        Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

        Let me say that Im sorry for all the confusion.
        I realize I have had some practical issues here that screwed up my results and its hard to perfrom analyzis when measurements are not reliable. One simple reason was the way I proped on the board.
        I now soldered some wires to critical testpoints so I can clamp on the probes and get reliable readings.

        So with the IC501 removed completely I can confirm that 15V indeed does NOT drop (loaded with 34Ohm, Resistors heating up) while the 7V line does DROP under load (same 34Ohm Resistor, drops to 4.2V, no heat)


          Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

          Puliing this up again, hoping ot get another great advice on how to proceed.
          I now have the oscilloscope here and Im learning how to use it. I have nothing to compare it to besides a very very old analog device that my dad used to have when I was a kid. This one is battery driven, digital, with auto range and auto hold. Its a Tektronics THS-720 if that brand/type is anything common.

          So to sum up the current state:
          loading the 15V line (measured and loaded over the 3 filter caps C503-505) the voltage stays stable.
          loading the 7 V line (measured and loaded between the Vin and GND Pin of IC501) the vltage drops. At the moment IC501 is completely removed.

          R_J suspected R501 (the 0.47Ohm Resistor on Pin 9 of T200) to be open => not the case
          or D205 to open under load. Testing the Diode unloded with my meter it seems okay.
          I dont know how to test the diode under load, but I think with the osci I should be able to.

          So from T200 comes some kind of AC current that is generated by IC200, right? Its not just a sine wave because IC200 does all kind of fancy stuff, like skipping cycles and so on but it is AC.
          The diode would be "cutting" one halve of the wave, because it blocks the current in one direction, but until a lot of filtering happens this still not a "flat line". Its waves cut in halve and it should be visible on the Oscilloscope.

          I will try to make the function of D205 visible, but to be hones I do not have high hopes that it is the faulty part.

          If anyone has another idea what I could test, I would verymuch appreciate it.


            Re: Panasonic TX-P50STW50 Power Supply no 5V (was clicking)

            By holding oscilloscope probe on top of transformer you should see pulses. I think you must have a feedback issue.
            I assume no responsibility for any stupid suggestions I might post.