LG with no Contrast no Brightness

Discussion in 'General Electronics Chat' started by burntfingers, Jul 25, 2011.

  1. burntfingers

    Thread Starter New Member

    Jul 20, 2011
    8
    0
    LG RT-29FB50VE

    Blue raster with flyback when grid increase at the flyback transformer, picture very faint, sound fine.
    No colour waves at microprocessor chip - pins 42 to 44.*
    Supplies, fine.
    No dry joints anywhere; components in the area all OK.

    Unfortunately, no diagram to help me; and the client is a good one, who always pays with no complaint.
    ...
    *Customer did not leave RC - I wonder if it's not at lowest levels...
     
  2. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Check the electro cap on the Video output transistors power feed, if dried out can cause this fault. Usualy on the board pluged on to picture tube neck.
     
  3. burntfingers

    Thread Starter New Member

    Jul 20, 2011
    8
    0
    Thanks for tip, but actually I'm misleading you here, because in fact the fault is nothing on the screen, only sound, unless I increase the grid voltage at the line transformer.
    Only so I can see the faint picture.
    Pins 42, 43, 44 of m/processor chip with no colour signal at all, but about 5v present.

    Could it be the chip?

    I've checked all relevant caps.
     
  4. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    This is the first time i am listening even TV also uses an up.....!!
    great.
     
  5. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Some of the Video chips are designed to kill the video OP when the tube gets too low in emmision, this feature has been around for sometime now.
     
  6. burntfingers

    Thread Starter New Member

    Jul 20, 2011
    8
    0
    That's so, but this set is relatively new, and still has good raster - increasing the 2nd grid control at the lopt.
    Nevertheless, I disordered pins 42, 43, 44 [RGB outputs] of IC, and still no signal is present - voltage about right.
     
  7. burntfingers

    Thread Starter New Member

    Jul 20, 2011
    8
    0
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