Atari 2800 or Sears Video Arcade II Composite Mod

[slaanesh]

I'm aware of superior s-video mods, but I'm having trouble finding exact information for modding an Atari 2800 or Sears Video Arcade II to composite.

 

I'm using the following as a guide: http://blog.tynemouthsoftware.co.uk/2018/09/atari-2600-ntsc-4-switch-composite-video-mod.html

 

Whilst the layout of the video/audio circuitry is similar to some other Atari models, it's not exactly the same so following other guides means that I can only identify 75% of what needs to be done.

 

I see the large red variable inductor and the transistor next to it and close to it the 18K resistor. Where is the 1.8K resistor?

 

 

Edited October 27, 2019 by slaanesh

[Cmherndon79]

Hi @slaanesh, did you ever figure this out?  Just recapped one of these and AV out was my next step.

 

The Atari Field Service Manual Rev 02 I have has reference to the CX2800 in the Tech Tips section and it has the schematics for the 2600 and 2600A, but not the 2800.  I know where to pull GND, +5 and Video from the RF modulator once removed.  Not 100% clear on where to pull the audio, nor which resistors to remove.  Fairly certain I need to remove the transistor next to the 2 audio caps that I replaced from the original 820pF polystyrene caps (I can't read the silkscreen for location, it isn't very clearly marked.   Looks like "Q2")

 

Think I can figure this out by comparing this board and the 2600A and some trial and error, but if anyone knows it'd save me the hassle

[slaanesh]

So in the end I used a Longhorn AV mod which also does s-video. I used the instructions found here: https://longhornengineer.com/category/projects/atari-av-mods/

 

However it looks they've since disappeared. I think you can find them from the Internet archive but if you can't I saved them so can re-post it... 

[Cmherndon79]

Thanks for getting back with me @slaanesh.  I appreciate it.

 

Anyhow, I got it working and I figured I'd better document it so when the next poor guy googles and finds this thread (as I did) they'll find what they need

 

Remove parts:

 

Q2 - Transistor

C10 - Capacitor

R14 - Resistor

R19 - Resistor

 

Connect audio to capacitor to the left of C10 that was removed if the system is facing you from the front (Can't read the location as the component is blocking the silkscreen

 

After that it's like any other VCS where you attach GND, +5 and Video to pins 1, 3, 4 in that order where the RF modulator was/is.

 

Probably if an admin reads this, it should be moved to Hardware if possible?

Edited February 1, 2020 by Cmherndon79

[slaanesh]

Hey awesome and of course, this mod will also work for Atari 2800 as it's the same thing. In fact that's what I actually have

[Cmherndon79]

Jealous you have an actual 2800.  I'd be keeping this one if it wasn't the Sears variety (I still think it's kinda cool, but I've got tons of 2600s).  I'll just be posting it up for sale instead.

[slaanesh]

The 2800 is actually no big deal. I also have a Sears Video Arcade II and there is literally no difference except for the badge. That's it.