Over the last few weeks, I’ve picked up several atari game consoles like the 2600, 2600 jr, and a 7800. I tried hooking them up via RF, but the quality is terrible on my TVs, so I went looking for composite mods.
I started with the 2600 junior. I built a single transistor amplifier and wired it in, but I was getting some strange behavior with the video. I then tried a more elaborate multi-amplifier circuit, but saw the same issues. I got frustrated and put everything back to stock. I still had problems with the video, so I switched to the 7800.
I know the 7800 was working, so at least I was starting from a known good state. I opened it up and removed the RF shield.
There are some components that need to be removed. There are several resistors, a capacitor, the channel selector switch, and the RF modulator. More info can be found here: http://www.retrofixes.com/2016/03/atari-7800-ntsc-composite-mod.html
I removed those components and wired in my single transistor amplifier. A similar amplifier design can be found in the picture below from here: https://www.thefuturewas8bit.com/index.php/2600_comp_mod
I added some RCA jacks to the rear using the existing RF modulator and channel selector holes so I didn’t have to drill into the case. I just used some washers to secure them in place.
I fired it up and it worked. I was getting decent video out. The circuit was working fine, so I guess there are other issues with the 2600 jr.
I did notice on some games, the video was a little dark, so I will need to make some adjustments. I may replace the circuit with a better one, but I was running out of time, so I mounted the board where the RF modulator was and put everything back together. I will come back and revisit this later when I have some more time.