Yet another Samsung 305T post - black screen w/backlight, occasionally works

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  • withalligators
    Badcaps Veteran
    • Jun 2013
    • 267
    • USA

    #1

    Yet another Samsung 305T post - black screen w/backlight, occasionally works

    Hey folks,
    I picked this neat monitor up from a recycling center years ago, and it worked fine for a long time. I know they are prone to T-con issues with the Altera chip, but I've yet to experience any symptoms of that going. I always perform scaling on the GPU though. It had occasionally thrown a black screen at me, that was usually reset by powering it off, and reseating the DVI-D cable in the sole input. I gave it to my brother who said the problem got worse, and it would be very difficult to get it to display a picture, it took lots of fiddling. As far as I understand him, it always needed a power cycle to work after reseating, which makes me think reseating was probably never necessary, and it was something internal. It worked immediately when I plugged it all in, but eventually gave me a black screen until I couldn't get an image out of it again. No on-screen display of any kind telling me to attach a cable or anything. Just black with backlight shining through.

    I took it apart and see at least one bulging cap on the power board, so I'm going to go ahead and replace all the Capxon stuff as a matter of course, though I can't seem to find any spec sheets for these caps so no idea on what ripple current I should be looking for etc.

    Obviously, this is where I should start, but is there anything else I should be thinking of?

    As far as the caps go, should I just order the best panny / nichicon / decent brand that is the same uf/v and same size?
  • withalligators
    Badcaps Veteran
    • Jun 2013
    • 267
    • USA

    #2
    Re: Yet another Samsung 305T post - black screen w/backlight, occasionally works

    With help picking the correct caps, I replaced all of the existing Capxons with equivalent Rubycons (there were 2 existing YGF rubycons I didn't replace as well as the large main cap) on the board. Unfortunately the problems persists. I tried multiple shutdowns, restarts, power cycling the monitor, and I got it to work one time after powering the monitor off and adjusting the DVI cable. It remained functional until I turned it off with the front button and turned it back on. Nothing after that. It doesn't seem like a faulty connection. There is also still no "no signal" notification that pops up with no DVI input, just a black screen with the backlights working. I have tried opening it back up and cleaning all the cable contacts with isopro and reassembling. No luck. I can try desoldering the remaining caps and testing tomorrow, but any other ideas? Wherever the error is, it is able to start the backlights, but not the T-con. Bad T-cons usually colorful affairs, but could this be caused by that?

    Comment

    • withalligators
      Badcaps Veteran
      • Jun 2013
      • 267
      • USA

      #3
      Re: Yet another Samsung 305T post - black screen w/backlight, occasionally works

      OK, I finally pulled the two Rubycons and the large main cap. They were at Vloss of 0.5 for the Rubys, and 1.0 for the large main. Not sure if this is acceptable or not. However, while thinking about this, something else popped into my head. This unit is behaving an awful lot like when I'm testing the backlights of a TV by unplugging the ribbon between main and PS. Except instead of just powering on as soon as it's plugged in, it is waiting for the power button to be pressed.

      Any ideas? Should I try baking the main board?

      Realizing I forgot pics of everything:

      https://photos.app.goo.gl/ZNfkfM5gwJ66iohZA
      Last edited by withalligators; 04-04-2022, 04:22 PM.

      Comment

      • rayliu11
        New Member
        • May 2017
        • 7
        • Canada

        #4
        Re: Yet another Samsung 305T post - black screen w/backlight, occasionally works

        Did you manage to fix this? I have a unit with the same problem, I suspect that it may be the EEPROM either on the TCON or the Mainboard

        Comment

        • withalligators
          Badcaps Veteran
          • Jun 2013
          • 267
          • USA

          #5
          Re: Yet another Samsung 305T post - black screen w/backlight, occasionally works

          I did not solve it. I think it was the daughter board and couldn't make heads or tails of it nor find a replacement. I invested too much time and gave up, nice as it was.

          Comment

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