Conecting composite signal to tv-tube.

Discussion in 'General Electronics Chat' started by alexi, Apr 19, 2013.

  1. alexi

    Thread Starter New Member

    Apr 19, 2013
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    Hi,

    I have a little raspberry project that I would like to build into a very old tv. Unfortunately there is no room and I'd like to take out the tuner board since I won't need it anymore. Is there a way to connect the Composite video signal directly to the tube or with minimal electronics.

    The tuner board seems to be separate from from whatever powers the tube, so I thought it might be possible to have the signals that drive the cathode ray come from somewhere else.

    Any ideas/recommendations?

    Alexi
     
  2. #12

    Expert

    Nov 30, 2010
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    You can't go in at the CRT because the horizontal and vertical oscillators are synchronized with the composite video. You have to go into an earlier stage.
    Senior moment...can't remember where composite video starts, and I fixed these things for a living!

    Here it is:http://commons.wikimedia.org/wiki/File:TV-block-diagram.svg
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    All I remember about my old TV was on the main PCB there was a RCA jack that took in the signal form the separate tuner module. The plug was sometimes soldered in place.

    There was probably baseband video on that main board too but I never needed to know where it was.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    The tuner output goes to the IF so you would need to find the detector output that generates the composite video after the IF. You would then disconnect the detector output and connect the composite into that point. If you don't have a schematic then you would likely need an oscilloscope to find the composite video detector output.
     
  5. Brownout

    Well-Known Member

    Jan 10, 2012
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    Look for a "line in" or "video in" jack. Most TVs that aren't ancient will have these. Otherwise, you'll have to find the video amplifier section. As stated, it will follow the IF section. This may be difficult to figure out.
     
  6. alexi

    Thread Starter New Member

    Apr 19, 2013
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    But then the avarage tv-tuner does output a composite signal? I was just hoping that would be the case :D

    That is good news!

    Too bad it's difficult to figure out where exactly that is happening on the board. Although as I have seen so far the tuner is often on a separate board.

    (the older tv's have an interesting design but no composite in, the newer tv's tend to be kinda ugly and do havea scart or composite... bummer).

    I better open that baby up and have a looksee.
     
  7. #12

    Expert

    Nov 30, 2010
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    It could be quite difficult. I have a 10 year old CRT television and the guts consist of 2 power supplies and a 40 pin chip...AND THAT WAS 10 YEARS AGO! Guess what's in 'em now.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    No. The output of the tuner is an IF signal which is a frequency down-converted version of the RF modulated signal. It is amplified by the IF amplifier section and then goes through the detector to generate the composite video.
     
    ErnieM likes this.
  9. bertus

    Administrator

    Apr 5, 2008
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