Nintendo Color TV-Game Composite Output Mod

Discussion of development of software for any "obsolete" computer or video game system. See the WSdev wiki and ObscureDev wiki for more information on certain platforms.
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famiac
Posts: 19
Joined: Mon Dec 26, 2011 5:22 pm

Nintendo Color TV-Game Composite Output Mod

Post by famiac »

This is an instructional post about how to get composite video from Nintendo's first consoles, including the Color TV-Game 6, 15, and Block Kuzushi. The same procedure is likely to work with the CTG-CR 112 racing game. Modding your console should improve its picture quality and improve its ability to interface with modern A/V equipment.

To understand what we're going to do, we start by looking at the CTG-15 schematic on the beforemario blog. Inspecting the image, it's readily apparent that the video game controller IC is sending component video to the RF modulator.

Image

Now, I don't want component video from a pong console, and i would prefer to use composite or Y/C. It's easy enough to tap the luma signal directly from the PCB and get a black and white image, but to get the chroma signal for S-video we'd need to either demodulate the RF output or modulate the color difference signals with the NTSC clock. Searching the terms "chroma modulator chip" leads us to the MC1372P, a Motorola chip that appears to do the same thing as the Mitsubushi M51342P and has a baseband chroma signal output, which is what we are looking for.

To replace the Mitsubishi chip, we would have to adapt the MC1372P's footprint and do some level-shifting, and this is where i was headed until i read a section on page 7 of the Motorola datasheet which states:
The RF modulator may be easily used as a composite video generator by replacing the RF oscillator tank circuit with a diode as shown in Figure 3.
Image
Seeing how similar these chips are, it would be silly not to try this, and i can attest that -- basically -- it works. There are just some pitfalls and technical issues to work through. The composite output from the modulator chip is weak and requires a buffer, and since we're not doing RF we need to separately tap the PCB for audio and buffer it. The Block Kuzushi units require an additional diode to drop the DC voltage on the Luma input to the modulator.

Ingredients:
  • 1x PNP transistor (2N3906), 1x NPN transistor (2N3904), 1x silicon diode (1N4148).
  • 1x 330Ω, 1x 10kΩ, 1x 100kΩ, 1x 2.2kΩ, 1x 22kΩ, 1x 27kΩ.
  • 1x 220uF, 1x 4.7uF, 1x2.2uF. all rated for 16V.
  • 1x 3.5mm audio jack
    if working on a Block Kuzushi unit, you'll need an extra 10k resistor and another diode.
    if working on a Color TV Game 6, you may want to mount a 5.5mm OD x 2mm ID barrel jack to use your famicom AC adapter with the console.
Procedure:

Working backwards from the RF modulator chip, remove the components circled in red:

Image

Install the new components in the video path to make the composite output circuit. Refer to the following figure.
Note that the schematic labels the power supply lines in an unusual way. One can think of -9V as GND so what's labelled as GND becomes +9V.

Image

You can tap audio from the small capacitor between the video game chip and M51342P pin 15.

Keep the grounding on your output connectors consistent. The machine is wired to use +9V for the video signal return path, so you need to do the same thing for the audio return path or risk damaging stuff, which i will not be liable for.

On a Block Kuzushi unit, the finished PCB should look sort of like this:
Image
The solder side is mirrored. not all the changes in the image are relevant to this mod.

Before testing the console, make sure the channel selector switch is set to channel 2. You may need to adjust the potentiometer on pin 13 of the modulator to get a picture.

Previews:
(HDMI capture card with 480p output from the Retrotink-2X Pro)

Block Kuzushi
Image

Color TV-Game 6
Image

Hopefully this information will make some part of video game history more accessible.
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TmEE
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Re: Nintendo Color TV-Game Composite Output Mod

Post by TmEE »

This is a clever idea ~
Pokun
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Re: Nintendo Color TV-Game Composite Output Mod

Post by Pokun »

Neat! I was under the impression that the RF circuit was inside the chip itself and the video signal couldn't be tapped.
flinn078
Posts: 3
Joined: Tue Jun 06, 2023 11:47 pm

Re: Nintendo Color TV-Game Composite Output Mod

Post by flinn078 »

i recently bought a junk color tv game 15 it only works there is a lot of interference on the screen i have already taken it to a repair shop but they couldn't fix the problem they only rotated the rf coils to the pal region so that it works on a pal tv. can this mod work on a tv game 15?
flinn078
Posts: 3
Joined: Tue Jun 06, 2023 11:47 pm

Re: Nintendo Color TV-Game Composite Output Mod

Post by flinn078 »

Does the old rd signal work with this mod?

If so i would like to do this 😄
flinn078
Posts: 3
Joined: Tue Jun 06, 2023 11:47 pm

Re: Nintendo Color TV-Game Composite Output Mod

Post by flinn078 »

Hey, its been some time since this is posted but i want to do this to my color tv game 15, my soldering skills are not that good also reading the schematics so can you post some pictures and a step through from your ctg-6 since those are literally the same.

Kind regards Flinn :D
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