Brand New Turbografx 16 RF Modulator Replacement Not Working

[Virtual Davey]

I have 2 TG16 units that do not display via their RF output. They both display fine if I tap into their composite pins. I read somewhere that RF modulators going bad in TG16 units are not unusual. I ordered a few and tried twice on 2 units with 2 separate, brand new, RF modulators. It doesn't seem to fix the issue. I can see a very scrambled, snowy picture of the game being displayed, but that's it. The RF modulators are very easy to install, so I don't think an incorrect installation is the problem. Is there something else on the board that would be causing this issue? Even switching the channel switch (Ch 3 or 4) on the modulator does not seem to make any difference, same image appears. It is also not the RF cord for I have multiple cords and have tested them with a working unit. When I have R-Type playing, I can sometimes make out the title screen, if I look really carefully.

[Dr Honda]

Since I'm not sure about the exact part you replaced it with... but there should be a couple chokes that need tuned. This is old-school analogue electronics.  Make sure you have a signal coming in... then tune the RF going out.   I just did a Colecovision the other day.  Same thing.   Oh... make sure to use a plastic screwdriver.  A metal screwdriver will cause issues, and you will never find the sweet spot.

[Virtual Davey]

Here is the exact part I'm using:
https://console5.com/store/jalco-mgb3-vu3401-rf-modulator-for-sega-systems-vcr.html
It seems the adjustment screw is for the audio carrier? Where are these chokes that need adjusting?

[Dr Honda]

The choke is right in the center.  Silver box with a black slug in the center.  You need to adjust it with the shield in place, and use a plastic screwdriver.

[Virtual Davey]

Thank you. I was under the impression (I was told) that the silver box with the black slug was an audio adjustment screw, which is why I never bothered adjusting it. Thank you for clarifying that. But once you have the RF modulator in position, and soldiered onto the board, reaching that choke  is impossible. I should perhaps soldier 3 wires to the 3 pins on the modulator (audio, video, 5v) and then soldiering the other ends of those wires into the 3 holes in the motherboard (where those pins would normally be soldiered to). That will give me temporary access to that adjustment screw.
EDIT: Upon further testing (I wired the modulator up temporarily as described above), I must say that the black dial does in fact control the sound, not the video. But I ran a wire from the composite pin (on the rear of the TG16 unit) to the video in on the modulator. I do get a a picture (and sound), but it seems too bright or colors washed out. When connected directly to the CRT ( no RF modulator in between ) the picture is bright and vibrant, perfect. Below are pictures using the composite through the RF modulator (washed out, colors are not vibrant):

[nyandeyanen]

Random-ish shot in the dark, if you put a 75 ohm resistor between the composite out pin to the video in on the modulator, does that bring the colors more into line?

[Virtual Davey]

Random-ish shot in the dark, if you put a 75 ohm resistor between the composite out pin to the video in on the modulator, does that bring the colors more into line?

I did as you suggested and used a 75 ohm resister. The picture is much better. If I didn't know any better, I'd say I'm finished. But compared to other TG16 consoles that I have, still a little too bright. Would I use a higher or lower ohm resister for a darker picture?
EDIT: I connected 2 75 ohm resistors in line and the picture appears perfect now.

[nyandeyanen]

I suppose a 150 ohm would suffice then, or you could try different values to get it perfect. I'm not sure why it's too bright coming directly from the system, but a resistor decreases the current going through it and that should make the image darker. The fact that there's no potentiometer to adjust the video strikes me as odd if the RF modulator is intended for the TG16, but adding resistors does the same thing (although it's more work to adjust.)