AV switchbox problem

Discussion in 'Home Theater Projects' started by Paul Spencer, Sep 15, 2006.

  1. Paul Spencer

    Paul Spencer Stunt Coordinator

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    I purchased two AV swithboxes for my brother in law for audio and component video switching. They are remote controlled units to replace his el cheapo manual slide switches. The cheapies worked fine, but the remote units stuff up component video! The image is ultra saturated.

    We tried all 3 units (mine included), they all have the same problem. Audio and composite video works fine, it is just component video.

    1) Can anyone pinpoint the problem here?

    2) How can I fix it?

    3) Can the switchbox be tweaked to work here as desired?

    Here is the switchbox, inside and out:

    [​IMG]

    [​IMG]
     
  2. ChristopherDAC

    ChristopherDAC Producer

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    "Ultra Saturated"? Sounds like the buffer-amplifier gain is 'way above unity. There ought to be a trimmer pot (variable resistor) somewhere on the board, which you can adjust to vary the gain. If you have an oscilloscope you can match input and output levels ; otherwise just fiddle with it until the image looks normal. With composite excess gain would not affect the image so much, probably, since it would be caught by the AGC on the TV.
     
  3. Paul Spencer

    Paul Spencer Stunt Coordinator

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    There are no trimpots at all. Could I put a dual gang pot on the video outputs to get it back to unity if this is the case? Say try a 10k pot?
     
  4. Paul Spencer

    Paul Spencer Stunt Coordinator

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    Well it turns out they are messing up my audio as well, it seems they are clipping on vocals! These things are a bad idea!
     
  5. ChristopherDAC

    ChristopherDAC Producer

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    Sounds as though the unit is defective. The buffer amplifiers should be unity gain.

    If you have an oscilloscope, you can watch the output amplitude and compare it against the input, which would give you a more solid idea what is going on. Are you sure you are using the right power supply?
     
  6. Paul Spencer

    Paul Spencer Stunt Coordinator

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    Yes, I'm sure I have the right power supply. I have bought three of these things. One for a purpose it's clearly not suited for (component video switching) and two for audio. Only one was used in my system. I had a problem with some very ugly distortion on female vocals in particular. I eliminated all other components and found that it was the switchbox. Needless to say, it was out! ... Not one of my best purchase decisions. I made the mistake of assuming that it put nothing in the signal chain.

    Unfortunately I don't have a scope, and with renovations going on, I know I don't have time to try to fix this one. I'll just have to live with the inconvenience of a manual switch for a while.
     

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