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Samsung HP-T5064 Ysus troubleshooting problem

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    Samsung HP-T5064 Ysus troubleshooting problem

    Hello all, I am working on a Samsung HP-T5064 50" flat screen plasma with a dark/blank screen and no picture. I have the issue narrowed down to the Ysus/Ymain board. The LED indicator on the board lights up indicating a problem. My Vs is good at 204V but VScan voltage at the test point on the board is about exactly half of what it should be, proper voltage should be -190V according to the label and I am getting -97V. The board# is LJ92-01490A/LJ41-05120A. I also measured voltages at the following test points:

    SIN_2 should be 0V
    OC2_C_2 should be 3V
    OC1_ODD_2 should be 3.5V
    LE_2 should be 0V
    OC1_EVEN_2 should be 3.5V
    CLK_2 should be 1.3V

    I have readings of 37V on every pin listed above.
    I removed and checked all the FETs (14 of them I think?) and 2 diodes from the heatsinks and they all tested good. I checked all of the caps and had 2 that were questionable so I replaced them. I also replaced both B13NK60Z transistors near the test points b/c they were surface mount and since I had them off to test I just replaced them with new ones. The problem doesn't change with the buffers disconnected and both Y buffers test good. I hope that someone can help me narrow this down to the cause and point me in the right direction. I'm not sure what ckts/components convert Vs to VScan. Thanks to all in advance.

    #2
    Re: Samsung HP-T5064 Ysus troubleshooting problem

    To simplify the concern, does anyone have a suggestion of what may be causing the Vsc voltage to be half, disregarding the other measurements?

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      #3
      Re: Samsung HP-T5064 Ysus troubleshooting problem

      Disconnect the wire that feeds power in and see if you are getting a higher voltage when not connected. -If so: this usually indicate that the power supply sees a short on the board it's feeding and is compensating for it.

      If you only have 90volts on the connector when unplugged then start testing the power supply board. I'd start tracing backward and testing where it drops, or figure out what is responsible for raising the voltage. Caps fail frequently and sometimes not visibly.

      NEXT:
      With the tv unplugged: test to see if you are getting shorts-assuming you've put the parts back on. And assuming you've read the Troubleshooting guide stickied at the top, and searched here and google for your tv model number.

      To test for shorts: stick one probe on the positive and one on negative input on the problem board. If you read 0ohms, or something close-you have a problem.
      Disclaimer: Don't trust a thing I say-I am frequently wrong!!!

      I have tons of spare parts, some used, some N.O.S. ham transistors and caps. Message me if you need any parts.

      Some of the things I've fixed:
      60" Vizio-bad LED's. iBook G4: Resoldered VCC Plug. Geo Tracker ECU: Swollen / Leaking capacitors. Windows Laptop: Soldered broken LVDS wires. Dryer: Burned contact on temp switch. Oven in R.V.: Bad contacts in relays-Exploded by the looks of them! Samsung Oven: Burned contacts on Relays. MSI Motherboard: BSOD-Swollen capacitors, bad graphics card, Moved SATA Input from SATA 1 to SATA 2 plug

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