Adding composite video input to old analog portable TV

Discussion in 'The Projects Forum' started by tinker95, May 15, 2017.

  1. tinker95

    Thread Starter New Member

    May 15, 2017
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    I found an old "Midland portable TV/Radio" that can receive AM/FM radio, as well as UHF and VHF TV (NTSC, since I live in the US). I want to be able to input composite video to the CRT for a retro screen.
    I took it apart (I understand the hazards of CRT's, and know how to discharge them) and luckily there are separate PCB's for the radio tuner, TV tuner, and TV and amplifier. The TV tuner is attached to the TV and amplifier board (a board which i believe drives the CRT) through a few ribbon cables, as well as something that looks like an old RCA phono plug. This caught my attention because this is the same plug used for composite video.

    I have been reading up on analog TV in an attempt to understand how this works more, so I can figure out how to accomplish my project. If I am correct, composite video needs only be modulated with a carrier signal in order to be broadcast. Thus, I figure that somewhere in the TV, after the demodulator, I can feed in a composite video signal and have it display on the CRT. I do not know if the TV tuner PCB is a demodulator or just isolates one TV signal. I have attached an oscilloscope screen of the output of this board. I also tried inputting a composite signal to where the tuner connects to the tv and amp board (using a raspberry pi) but still got white fuzz on the screen.
    Am I approaching this correctly? IMG_20170515_085549215.jpg IMG_20170515_085828624.jpg IMG_20170515_085853599.jpg IMG_20170515_085617944.jpg IMG_20170515_090144233.jpg
     
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    I would just use a cheap external RF modulator. The odds of finding a signal point on the old TV that's directly compatible with a composite video NTSC signal is low.
     
  3. tinker95

    Thread Starter New Member

    May 15, 2017
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    Thanks for the quick reply. There is no input for a TV signal with this TV, it just has an antenna. Perhaps wire the modulator to somewhere on the board?
     
  4. ericgibbs

    Moderator

    Jan 29, 2010
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  5. LesJones

    Well-Known Member

    Jan 8, 2017
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    A modulator converts composite video to an RF signal modulated with the video so it just connects in place of the antenna. Most modulators also have an input for the audio signal as well.

    Les.
     
  6. tinker95

    Thread Starter New Member

    May 15, 2017
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  7. wayneh

    Expert

    Sep 9, 2010
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    I sold the last RF modulator I had a few years ago on eBay for under $5. You're free to have fun any way you want, but I'd certainly recommend seeing what's available before building one. A DIY one will cost more than a commercial one and take a bunch of time.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Depends upon your definition of "fun" I suppose.
    That looks to be a lot of work and expense (especially the PCB, since you don't want to build this on a perf board), and getting everything to work properly at those frequencies can be tricky.
    But to each his own. :rolleyes:
     
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