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simon.plata

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  1. simon.plata
    Searching for the model number C011885 REV F engraved in the bottom side, it could be Vangard. http://www.timjenkinsweb.com/Atari/chips/chips.aspx
  2. simon.plata
    Very clever solution, I think it will work without issues. The additional second stage should draw less than 70mA, so is not a problem for the 7805, as far the heat sink could dissipate the additional power. In the worst case the 2600 will shutdown because the thermal protection of the 7805, until it cools down. Normally a 7805 does not burn itself because is current limited and thermally protected.
  3. simon.plata
    Not really, maybe you're confused because first stage is voltage follower, but second stage is a common emitter. Output impedance is defined by the last stage, in this case, a common emitter.
  4. simon.plata
    My apologies, I'm very glad helping you. However I have been very busy this days at work. I will come back when I have a breath.
  5. simon.plata
    I'm sorry to contradict you, but the output impedance of the common emitter BJT amplifier is equal to: Zo = RL || ro Given ro is very high, the output impedance is very close to RL. Figure 9.2.4 Common emitter or source small signal models. (Source: https://wiki.analog.com/university/courses/electronics/text/chapter-9)
  6. simon.plata
    It is working as I expected. You need to adjust the gain trimmer after changing the output resistance value. Did you? May be I need to recalculate the other resistors to avoid saturation of the amplifier.
  7. simon.plata
    It should work, however it could be necessary to adjust the gain trimmer every time you switch (change) the resistance.
  8. simon.plata
    I should give it a try. It's almost impossible to be cheaper built than the original Atari :-). A bad bypass capacitor could make also the image darker. Also, Yes, it is possible to "power it up a bit" and use a passive splitter, it's a matter of impedance matching. You will need to figure out which is the input impedance of the splitter and then match the output resistor of the AV mod to this value. After that you can fine tune it adjusting the amplifier gain with the trimmer.
  9. simon.plata
    Video interference could be produced by a noisy power rail, and this is very common in old equipment due to electrolytic capacitor aging. I suggest to check with an oscilloscope the 5V power rail and verify it does not have ripple. I do so, then replace the bypass capacitor.
  10. simon.plata
    Excellent, lowering the trimmer value should augmentate the gain until you get the desired image after the splitter.
  11. simon.plata
    Did you built the one stage or the two stage version? With one stage the gain is in the edge, with two stages you may have more room to compensate the coupling lost with more amplitude gain.
  12. simon.plata
    It should have enough "power" given that the output impedance is matched to 75 Ohm which is the standard for video. So any splitter which works with standard output video, should work with this mod.
  13. simon.plata
    @the_crayon_king made a very good point, you could still have audio signal interference. Did you removed ALL the components indicated in the instructions? Otherwise audio signal could still have a path to mix with video. Also, the indicated components needs to be removed in order to leave a clean chroma and luma signal. The RF oscillator is still in place? Or was removed? I believe all the above makes sense because both the mods you referenced as working properly, are taking signals directly from TIA pins. Bests,
  14. simon.plata
    Ok, Colors and saturation looks good, then I can say the mod is working properly. The issues with the image are related to gosthing and image post processing by the TV DSP. BC548B/C and BC558B/C are good replacements. Be sure there are BC5x8B or C, the last letter defines de hfe of the transistor. Letter A or no letter are low gain devices. I suggest the following: The 75 Ohm resistor is very important. Be sure it's 75 Ohm +/- 5% The video cable is the responsible of most of the problems. Please ensure you're using a good video cable and connectors. Check cable resistance, should be less than 1.5 Ohms. Check ground. Try to find a CRT TV set (old TV) and check the video image on it. Several new LCD/LED TV sets have several image processing algorithms that can distort the video. If the gain change didn't affect the brightness, it's an indication that the TV DSP is normalizing the video and further post processing is being done. After checking the image in a CRT and tuning the gain, go to your LCD/LED TV set and disable ALL the image processing or enhancing features. This should improve the image. Let me know how it works for you. Bests,
  15. simon.plata
    Typical audio line input impedance is 10K and line output impedance is 100 or 600 ohms. Due to short distance of the cable in comparison to the wavelength, impedance matching is not required. For maximum audio signal level you may choose 100 to 600 ohms for R9. However I prefer to use 10KOhms (same as line input) for short circuit protection and to avoid input saturation. Please let us know how it works for you and the video results. bests!
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