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Thread: Genesis Model 1 no video output[fixed] Help with S-Video!

  1. #21
    Great Puma (Level 12) jb143's Avatar
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    Quote Originally Posted by DogP View Post
    I did terminate it with a 220 ohm resistor because the slew rate of the falling edges was a little slow, causing a slight jitter on the screen.

    But yes, a good op-amp circuit is nice as well, though this simple transistor circuit certainly has its uses.
    You know, I was actually looking up specs on the transistors being used to see if a too low slew rate could be causing people issues. I know from experience that the same exact part number from different manufacturers can have different slew rates. This was for op-amps though. Transistors don't list it, I guess because it has more to do with the final amp design. You would probably need an oscilloscope to figure out what it is though.

    If anyone is wondering, slew rate has to do with how an amplifier handles quick changes. If an amp has a low slew rate then a fast changing signal can get distorted. In video applications you typically want a higher slew rate. Same for bandwidth but the general purpose transistors look to be high enough.

    I guess I'm just a bit leery of using general purpose transistors in a very simple circuit for video applications. But hey, if it works it works. But since people have been having issues between different TV's, and the instructions basically say randomly use different values for the parts until it does work, then I'd say a better alternative would certainly be nice.
    "Game programmers are generally lazy individuals. That's right. It's true. Don't let anyone tell you otherwise. Since the dawn of computer games, game programmers have looked for shortcuts to coolness." Kurt Arnlund - Game programmer for Activision, Accolade...

  2. #22
    Pretzel (Level 4) APE992's Avatar
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    A higher slew rate would be nice though the transistors I used seem to handle themselves just fine. At least I don't notice any problems but that doesn't mean my display isn't hiding them. After doing some calibrations I found it was losing about 2" worth of picture to overscan on all four sides. Likely normal but it doesn't please me.
    I fix things. You name it, I'll work on it. Want something modded? Recapped?

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