I recently purchased a TI-99/4a. Well, 2 actually. Both work, but I only have one RF modulator. I ordered a composite adapter, but that hasn't arrived yet. Both work on the RF modulator, but the video output is very poor. The audio seems to be working perfectly. It looks like it can be opened, but I don't want to damage it to find out nothing can repaired, as it is in a nice condition. Are there any capacitors in the RF modulator or anything else that can be serviced?

  • Typically an RF modulator would have settings for different channels - e.g., channel 3 or channel 4. Things have changed a bit with digital TV, but still worth trying any different settings available, if you have not already done so. Commented Aug 1, 2022 at 22:13
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    @manassehkatz-Moving2Codidact: Many RF modulators had an adjustable tuning coil which could be calibrated and then a switch that would load the oscillator circuit by a non-adjustable amount. A modulator that was calibrated to be perfectly in tune for one channel would thus often be less well in tune for the other.
    – supercat
    Commented Aug 1, 2022 at 22:18
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    I switched from channel 3 to channel 4. It is a massive improvement. However, its still a bit fuzzy. I guess I will wait till the composite adapter comes in to see how much better it can be. Once I confirms the composite cable works, then I will open up the RF modulator to see if there are any potential adjustments or hardware replacements.
    – Keltari
    Commented Aug 1, 2022 at 23:59
  • Are you using an old analog monitor, or are you going through an analog-to-digital converter to a digital monitor?
    – Jon Custer
    Commented Aug 2, 2022 at 15:10
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    Please be aware that video sent over RF is bandwidth-limited and will make screens fuzzy. This is a technical limit you cannot avoid. Would you mind to add an image to your question for us to see? It was and still is the best to connect the video signal directly. Commented Sep 26, 2022 at 6:15

1 Answer 1


While not directly answering my own question, this is the solution I ended up doing:

I just ended up buying a composite adapter, which works great. I decided against opening up the RF modulator, as I dont want to damage it. While I can fix various electronic problems, I am not an electrical engineer and I do not want to damage the modulator visually or electrically. Other than being a little fuzzy, it works. Since I dont plan on using it, why risk breaking it? I dont think its worth it. If I ever end up selling the TI-99/4a, the next owner can decide what to do with it.

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