LCD tv diagnosis assistance needed

Discussion in 'General Electronics Chat' started by Ironus, Jan 21, 2015.

  1. Ironus

    Thread Starter New Member

    Jan 21, 2015
    Service manual for chassis says : pins 3,5 on IC02 measure 3.3vdc. IC02 is connector from ir/pwr switch to ssb. Should I be connected to earth ground or circuit ground for measuring? Using circuit ground I get 3.12vdc on first and 3.17vdc on second. Are these measurements within acceptable parameters or should I back up and regroup?
    IMAG0373.jpg Screenshot_2015-01-21-14-57-24.png IMAG0373.jpg Screenshot_2015-01-21-14-57-24.png
  2. crutschow


    Mar 14, 2008
    You should measure most voltages to circuit common.

    Those voltages seem slightly low but are close to the typical 3.3V ±5% tolerance or 3.135V to 3.465V so are probably okay.
  3. bwilliams60

    Active Member

    Nov 18, 2012
    Just curious. where did you get the service manual from. Those are hard to come by. Any chance of getting a copy? You can PM me if you like
  4. Ironus

    Thread Starter New Member

    Jan 21, 2015
    Ty, crutschow. Couldn't remember from high school electronics (15 yrs ago). I have a few things left to try but if v is within tolerance then all other points have been too and evidence suggests ssb at this point. I hate to replace the whole board but this has led me probably to the end of my know-how.
  5. Ironus

    Thread Starter New Member

    Jan 21, 2015
    LED worked when I plugged it up originally, stopped working after about an hour of being plugged up. LED blink method didn't work at all. Have no way to enter service modes as I cannot get tv to do anything. Psb seems to be fine but after that I haven't the equipment to further test.
  6. Evil Lurker


    Aug 25, 2011
    Well, this is what I would do...

    1. Disconnect the logic board from the PSU, check the ESR of the output filter caps and the output voltages on each rail. If everything looks good there, move on to the main logic board.

    2. There are a bunch of DC-DC converters on the logic board as indicated by the shielded "box" inductors in the upper right hand corner. Check the output voltages of each of those. One of those caps looks "shinier" on top for some reason. It is possible that one of those caps has failed. I'd suggest checking the voltage across the caps, preferably after any low pass filter (which should be indicated by any smaller inductors with lower inductance ratings).

    3. Inspect the main logic board and any smaller boards for any fuses marked "FB". Make sure none of them are open.

    4. If everything appears ok, then you start checking voltages on the VCC pins of your IC's. If they look ok check for any cold solder joints around any high voltage inverter transformer, or better yet dab a little flux around the pins and reflow them with your soldering iron. That was the only thing wrong with the 42" flatscreen in my bedroom... a cold solder joint on one of the inverter transformers. Also reseat any flat ribbon cables.

    5. Break out the scope and see if you can figure what is going on, and if you don't have one perform a hail mary maneuver and reflow the IC's starting with the boards that get the hottest.

    6. Start replacing boards.