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How do diagnose Samsung 215TW monitor?

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    How do diagnose Samsung 215TW monitor?

    I have a pair of Samsung 215TW monitors. They both had bad caps. I replaced the caps on power board 1 in monitor 1 and tested it. Turned on and then back light shut off right away.

    I replaced the caps in power board 2 and tested it in monitor 1, same problem, back light turns off.

    I then put repaired power board 1 into monitor 2 and tested it, monitor 2 works flawlessly with power board 1. I then swapped repaired power board 1 with repaired power board 2 and tested monitor 2, still works flawlessly.

    Tried testing both of the power boards back into monitor 1 and still had light shut off within a second.

    Now I am trying to get monitor 1 running.

    Putting either repaired power board into the monitor does nothing. Blue light comes on and screen flickers but then goes dark with image showing if you hold a light to it.

    I then tore apart a Samsung 24 inch monitor that had a smashed screen and known good backlights. I then tried swapping out the backlights on the 215tw with the known good lights and the lights turn on but turn off within a second. However the known good lights on the 24" samsung are MUCH bigger than the 21" samsungs. Is that an issue?

    I'm just not sure where to go now. I have 2 known good powerboards and the same symptoms on the bad monitor with either board.

    I'm just thinking that maybe the 24" bulbs are too big and the driver circuit can't drive them. I can go back to the recycling center and look for a smaller smashed monitor to rob some backlights from, should I or would that not make any difference?
    Last edited by bobotech; 04-11-2014, 05:17 PM.

    #2
    Re: How do diagnose Samsung 215TW monitor?

    It could be the feedback and control circuitry sensing something and sorting down.

    If you're worry about the 24 inch monitor back-lights drawing too much current; while not try reducing the brightness of the back lights (if possible) and see whether your PSU can then handle the power needed.

    Alternatively, you may troubleshoot as well by connecting the back light(s) to the PSU without the LCD plastic back cover and better-off, with one or both of the back lights removed from its compartment in the monitor. LCD / back light should stay-on if back lights are good and PSU is faulty.

    I've as well be expressing two sec to black on 3 monitors using EADP-43 AF PSUs and only work (kind of last on though goes off if move around) when i did the above (second paragraph). I've tried all the 2 sec to black troubleshooting work-rounds to no avail but i know the culprit is the PSU, as powering the 3 monitors with a known working EADP-43 AF PSU and other different PSU brands, have no 2 sec to black issues.

    Interestingly, i measure the DC voltage (depending on your PSU, the CCFL connectors pins carry both ac and dc -- you may experiment and see which) of the four back lights of all 3 monitors reveals ~3V each on two back lights connected to one CCFL transformer and ~1 and 6V across the other two back-lights connected to the other CCFL transformer.

    Swapping the back lights have no effect on the connectors with 3V but the 1 and 6V swaps on the other connector -- with one of the back light bulb off, if not almost / flickers while the other bulb is very bright confirming the power disparity issue from that transformer connectors. By the way, it's not dry joints, bad tracks nor the CCFL transformer as the output resistances (impedance) were spot-on ~ 515 ohms each and for desperation sake, even re-soldering /replacing the CCFL transformer with good ones had no effect. I traced the voltage disparity to be across small signal diodes supplying the back light lights but all diodes tested ok with a multi-meter diode testing.

    However, i'll replace suspected diodes when i have time and see if it helps. The diode could pass when un-powered but faulty when powered, as a result of thermal issues / cold joints as a result of aging. A thermal oven /dryer or freezer/cooler can be handy in such cases.

    I might seems to hijack your thread but i thought sharing my experiences might be insightful to your case and others.

    Good luck and smile over any typos -- as usual

    Comment


      #3
      Re: How do diagnose Samsung 215TW monitor?

      How about the main logic/scaler board? Can you move the logic/scaler board of #1 to the #2 chassis.
      Or leave the power supply 1, logic/scaler board 1 on #1 chassis and connect the lamps connectors of #2 to it and see if it will stay on.
      Or make a pair or two pairs of test lamps:
      https://www.badcaps.net/forum/showthread.php?t=19987
      Last edited by budm; 04-11-2014, 09:56 PM.
      Never stop learning
      Basic LCD TV and Monitor troubleshooting guides.
      http://www.badcaps.net/forum/showthr...956#post305956

      Voltage Regulator (LDO) testing:
      http://www.badcaps.net/forum/showthr...999#post300999

      Inverter testing using old CFL:
      http://www.badcaps.net/forum/showthr...er+testing+cfl

      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
      http://s807.photobucket.com/user/budm/library/

      TV Factory reset codes listing:
      http://www.badcaps.net/forum/showthread.php?t=24809

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