Atari 2600/7800 Composite MOD

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rubber_jonnie
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Atari 2600/7800 Composite MOD

Post by rubber_jonnie »

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 many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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exxos
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Re: Atari 2600/7800 Composite MOD

Post by exxos »

: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:
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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie »

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 many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Atari 2600/7800 Composite MOD

Post by exxos »

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 5874 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...
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie »

Ahh, cool I will have a look, thanks.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Atari 2600/7800 Composite MOD

Post by exxos »

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
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https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie »

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 many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Atari 2600/7800 Composite MOD

Post by exxos »

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 5867 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 :(
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Atari 2600/7800 Composite MOD

Post by rubber_jonnie »

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 many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Atari 2600/7800 Composite MOD

Post by exxos »

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:
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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