2600 Composite Mod

[R.Cade]

Hi guys,

 

I recently got out my old 4-switch Vader that had an old original Cracknell mod in it. It was very overdriven and wavy on modern TV's, so I decided to pull it out and replace it with a simple transistor mod from the RF box wires like this:

 

http://www.made-by-b...php?f=101&t=842

 

I think this mod is also on AtariAge somewhere, and someone seems to be selling one on eBay.

http://www.vintagega...-guide-4switch/

 

It is very similar to the "Easy 7800 mod" here:

http://atariage.com/forums/topic/127926-easier-7800-composite-video-mod/

 

Even though video is crystal clear, it seems the contrast or brightness is off. If I run Pac-Man, the maze is not yellow, it's brown. The maze background is super-bright blue, instead of darker blue. When I run the game on Stella, it is quite different. The pot inside the 2600 cannot turn the colors anything like that of the emulation.

 

I hooked up my 2600 Jr. with RF and find that it's a lot brighter, but Pac-Man maze still seems "wrong" colored.

 

Am I just spoiled by emulation all these years and the Vader won't look as good, or is this just a bad mod since it's based on the existing RF box signal?

Edited August 4, 2013 by R.Cade

[pimpmaul69]

that is the peoblem with composite mods. some games will look right with adjustment, some wont. colecovision is the best way to go. cheap and easy as hell composite mod. crystal clear picture and colors are perfect on everything on coleco games and atari adapter.

Edited August 4, 2013 by pimpmaul69

[R.Cade]

that is the peoblem with composite mods. some games will look right with adjustment, some wont. colecovision is the best way to go. cheap and easy as hell composite mod. crystal clear picture and colors are perfect on everything on coleco games and atari adapter.

 

Then I have to deal with the cranky Colecovision hardware...

[pimpmaul69]

Then I have to deal with the cranky Colecovision hardware...

cranky? whats the problem you have? also most of the coleco is not used for tha atari except the video output.

[R.Cade]

I didn't really want to talk about Coleco repairs in this thread, but possible tweaks to this composite mod, if possible. Thanks, though. I have two Adams and two CV's. I don't think any of them work right at the moment- various issue.

[Greg2600]

could be your TV. My 2600 composite mod looks differently on CRT vs. LCD televisions.

[iesposta]

I have done this transistor, 3 resistor on a 7800 for composite. Used scrap parts I had around. When I couldn't get the exact resistor value, I used the closest I could find. A hundres times improvement from RF, and I didn't notice any differences in game colors.

The same transistor is used for the Sega Genesis S-Video mod, and again I used what was around. That came out real good also, just slight vertical jail bars. Did the same mod AGAIN for the Sega Genesis 32X attachment, and that S-Video is even better than the Genesis S-Video.

I never tried this type of mod on an Atari 2600, as the first one I modded was a 4 switch with a Longhorn Board from electronicsentimentalities, and next when I wanted a 6 switch with S-Video I got the batari AV board from the same seller.

Did you find instructions specifically for the 2600?

The 7800 involves removing the RF and some resistors and replacing? others. If parts of the video circuit unit are left in, it will cause the composite out to get worse.

[R.Cade]

Sorry to necro-bump my old thread, but I had some time this holiday to try to fix this.

 

I'm not sure where the 2.2k/3.3k bias resistors came from in this design. As far as I know, they are not needed- all they do is reduce the amount of gain from the simple transistor amp.

 

My changes:

Remove the 3.3k from video out to ground

Replace the 2.2k from video out to 5v with a potentiometer - this is not really needed, but you can adjust it if you want. I used a 20k, but it's almost all the way up.

Make sure C215 is removed, otherwise you'll have bad ghosting.

 

Now, other than a little "graininess" in the video (vertical banding), it perfectly matches the brightness and colors of the Stella emulator.

Pac-Man is yellow in an orange maze with dark blue background again.

 

Edited December 27, 2015 by R.Cade

[spawnshop]

I have this same mod, but I haven't tested PM in it, so I will check it out. If so, I will try your adjustment on it.

Thanks for the update!

[R.Cade]

It can be improved a little more also. I wasn't fully happy with the colors- they were a little light.

 

Remove the resistor to the left of C208 (where you connect audio). Replace it with a jumper... (straight connection).

 

On my board, there was a resistor jumping two pins of the TIA. I think this was to increase richness of the color (it is posted elsewhere on the forums).

Remove this and replace with a jumper (straight connection). Every board seems to be a bit different. Were there really 16 revisions?

 

Now colors are richer, and the edges aren't quite so harsh (white dots).

 

This is for my 4-switch vader... I did a similar mod to my Junior and they both look great now.

Edited December 27, 2015 by R.Cade

[Micheloni2600]

Curious. I have been doing this mod and it looks well! But I am wanting to try it on a six switch. Now as far as C215 that is removed for less ghosting is that the same part removed on a six switch board? Because it appears to be a green chicklet in place of C215. Hope to hear back soon as I'm curious. Same with making a jumper by removing resistor to left of where audio is tapped. In this case being R225?