Yet Another 2600 Composite Mod Help Thread

[Videlen]

I'm attempting to mod my Sunnyvale Heavy Sixer with a composite video mod. I'm following the quick and dirty single transistor composite video amplifier mod, the schematic is attached. I've built it twice with two different transistors to rule out the possibility of bad parts. I've removed the RF modulator and I'm attaching this amp to the composite video pin that used to go the RF modulator.

 

So far I've removed Q202, R213, and the large pink inductor near Q202. On the screen, I'm getting a dark black snow and the TV think's it's a PAL video signal (it's an NTSC Atari). I've also posted the composite video waveform I've captured with my scope. Without the mod, it's about 1.2V peak to peak and the horizontal blank looks like a fang rather than a rectangle.

NewFile9.bmp

NewFile11.bmp

NewFile10.bmp

 

With the mod, for some reason the signal becomes less pronounced, at about 200mV peak to peak.

NewFile12.bmp

 

This is what my main board looks like right now

 

I should also note that on the secondary board of the Atari (the one with all the switches and the RF modulator), my RF modulator only has 3 pins. All the tutorials I've found online show an RF modulator with 5 pins. The 3 pins on mine are +5V, GND, and (I assume) composite video.

 

Can anyone help me with this mod? Did I forget to remove a component from the main board or something?

 

[cwilkson]

You have to load the amplifier with something. Try connecting a 75 Ohm resistor from the transistor's emitter to ground and report back here. (from "C-video out" to "RCA GND")

Edited June 5, 2018 by cwilkson