Atari 2600/7800 Composite MOD

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rubber_jonnie
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Atari 2600/7800 Composite MOD

Post by rubber_jonnie » Fri Feb 23, 2018 2:19 pm

There is a great article here about 2600 composite mods, so I've ordered a bunch of bits to make one (Or maybe more :o )up.

https://www.thefuturewas8bit.com/index. ... 0_comp_mod

Will let you all know how I get on, and since it's supposed to work with both the 2600 and the 7800, of which I have both. It'll also allegedly work with the ZX81 too. I've got one with terrible video out, so that may happen as well.

As usual, I'll get a load of pics while I do it, and will post them up here.

If it all works out, and anyone is interested in an assembled board, I will probably make some up and sell them at cost price plus a small amount for postage, if anyone is interested.
Collector of old Atari things:
800XL + Ape Warp mod, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg) + Gotek, 1040STFM + Vortex ATOnce + Gotek, 1040STF long button floppy, 4160 STE with Gotek and ROM switcher, 4160STE with 32Mhz booster, ROM switcher and CosmosEx, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

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Re: Atari 2600/7800 Composite MOD

Post by exxos » Fri Feb 23, 2018 2:27 pm

:bravo:

I did see that that a few days ago. A lot of them seem to go down the similar route. What I don't really understand is why the transistors even needed because there is a buffer chip in the video with the resistor ladder anyway. A lot of them seem to hack to bits a lot of the circuit, then rebuild basically the same thing which seems a bit pointless to me :shrug:

In any case looking forward to your testing and results :thumbup:
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie » Fri Feb 23, 2018 2:33 pm

exxos wrote:
Fri Feb 23, 2018 2:27 pm
:bravo:

I did see that that a few days ago. A lot of them seem to go down the similar route. What I don't really understand is why the transistors even needed because there is a buffer chip in the video with the resistor ladder anyway. A lot of them seem to hack to bits a lot of the circuit, then rebuild basically the same thing which seems a bit pointless to me :shrug:

In any case looking forward to your testing and results :thumbup:
:goodpost:

Whilst I can build stuff with relative ease, I have to trust to others that the dev work is good, because without the electronics knowledge and understanding, I just can't verify if it's a good design. Wish that wasn't the case, 'cause I think you do some amazing dev work, and wish my skills were as good.

Good thing is that the parts are ridiculously cheap, so building a couple for my machines isn't too expensive. I would always be open to options about different ways to do it, and trying them.

Do you have any thoughts about options?
Collector of old Atari things:
800XL + Ape Warp mod, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg) + Gotek, 1040STFM + Vortex ATOnce + Gotek, 1040STF long button floppy, 4160 STE with Gotek and ROM switcher, 4160STE with 32Mhz booster, ROM switcher and CosmosEx, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

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Re: Atari 2600/7800 Composite MOD

Post by exxos » Fri Feb 23, 2018 2:46 pm

This caught my attention as well ...

http://thevowel.com/blog/2012/06/29/upg ... tari-2600/


Mostly I was just looking at circuit diagram itself... Seems difficult to work out as a seems to be multiple revisions which all look very similar, but the part numbers a very much different.. Not hundred percent sure what all the differences all of the diagrams or even correct...

Schematic_Atari2600_Junior_PAL.gif
Schematic_Atari2600_Junior_PAL.gif (52.99 KiB) Viewed 897 times

Basically the TIA outputs all the necessary video signals, then basically wire them all in parallel to generate the signal .

If you look there is a buffer 4050 there with the Vista ladder where at that point should basically be the composite signal. However it is possible the resistor values may be too low, which could be why people using a transistor to amplify the signal.. Course there is two ways of looking at it, as you can either add the amplifier, or replace the resistors with lower value ones like 1K,2K,4K kind of thing.

In a lot of mods I think Q4 gets chopped out as well . It gets a little messy with the colour output from the TIA.. That could possibly need slight tweaks as well.. But of course I have not looked into this much yet.. I think there was a sight which basically did what I propose here, but I did not seem to bookmark it :roll: I will try and find it later...
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie » Fri Feb 23, 2018 3:05 pm

Ahh, cool I will have a look, thanks.
Collector of old Atari things:
800XL + Ape Warp mod, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg) + Gotek, 1040STFM + Vortex ATOnce + Gotek, 1040STF long button floppy, 4160 STE with Gotek and ROM switcher, 4160STE with 32Mhz booster, ROM switcher and CosmosEx, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

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Re: Atari 2600/7800 Composite MOD

Post by exxos » Fri Feb 23, 2018 3:14 pm

I did look into this several years ago as well.. But basically I used a video generator chip, I think it was to generate RGB signals for scart. I can't remember what chip it was, or I can remember is the results were horrific and I just gave up with it.

This page has a few things tried out..
http://www.r3uk.com/index.php/tech-tips ... video-mods


This page has basically what I was thinking off.. Or release one of the ideas.. It is in the page I looking at before but it is basically the same idea..
http://www.console-corner.de/videomod.html
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie » Fri Feb 23, 2018 3:23 pm

Actually, reading what you wrote made sense, well explained :dualthumbup:

One thing I don't understand is, if the signal is available there, why remove the modulator?

As for Q4, I'm assuming that's an audio amplifier that feeds into the modulator, so why would you want to remove it?
Collector of old Atari things:
800XL + Ape Warp mod, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg) + Gotek, 1040STFM + Vortex ATOnce + Gotek, 1040STF long button floppy, 4160 STE with Gotek and ROM switcher, 4160STE with 32Mhz booster, ROM switcher and CosmosEx, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

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Re: Atari 2600/7800 Composite MOD

Post by exxos » Fri Feb 23, 2018 3:31 pm

rubber_jonnie wrote:
Fri Feb 23, 2018 3:23 pm
One thing I don't understand is, if the signal is available there, why remove the modulator?
I think it is to reduce interference on the video signals... As to if it actually helps or not I don't know.. But it makes sense to remove it..
rubber_jonnie wrote:
Fri Feb 23, 2018 3:23 pm
As for Q4, I'm assuming that's an audio amplifier that feeds into the modulator, so why would you want to remove it?
Same thing I presume, looking at this diagram...

compositemod.gif
compositemod.gif (4.45 KiB) Viewed 890 times

Anything else connected to the line is likely just going to cause problems...

I would probably go with that diagram myself... But I would also be tempted to replace the 4050 with probably a LS chip which will have faster switching and a little bit more drive current.. A quick look the pinout seem to be somewhat different so it wouldn't be a straight swap :(
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie » Fri Feb 23, 2018 3:36 pm

exxos wrote:
Fri Feb 23, 2018 3:31 pm

Same thing I presume, looking at this diagram...
I may try both approaches, see what turns up, as I have a drawer full of bits to tinker with.
Collector of old Atari things:
800XL + Ape Warp mod, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg) + Gotek, 1040STFM + Vortex ATOnce + Gotek, 1040STF long button floppy, 4160 STE with Gotek and ROM switcher, 4160STE with 32Mhz booster, ROM switcher and CosmosEx, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

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Re: Atari 2600/7800 Composite MOD

Post by exxos » Fri Feb 23, 2018 3:39 pm

rubber_jonnie wrote:
Fri Feb 23, 2018 3:36 pm
I may try both approaches, see what turns up, as I have a drawer full of bits to tinker with.
That would make my life a lot easier ;)

If the 4050 was removed, little plug-in board could be put there tweaks and fixes for the video drive.. Though would still need some wire links for the colour and audio signals still makes it a little bit messy with wires..

Any other solution could be to design a larger plug-in board which would plug into the TIA socket, and plug the TIA into the add-on board (kind of like the ST shifter with RAM mods do) and then just basically rebuild the video circuit that way.

But I have no idea if there is physically enough room to do that :shrug:
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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