CD4050 A/V mod on PAL atari 2600

Blackegg13 · May 7, 2012

I'm realy sorry for resurecting so old topic, but I'm getting desperate.

Last couple months I was trying to convert my 6 switch Atari 2600 to work over composite video. I had tried few mods and only one worked with bad video quality. I was considering buying ready one, but they are all from US and I'm not sure if they will work on PAL console. One from this topic was last one I have tried. I have redesigned board that mamejay have posted here to accommodate screw terminals.

My problem now is fact that picture I'm getting is black and white. If I connect chroma to output directly I got colours but with rubbish quality. If it's connected to terminal on mod board there is no colour. What I'm after is where I got it wrong. I have attached diagram I done and 2600 motherboard diagram with points (green) where i connected wires. Red crosses are the elements I removed.

I will appreciate any help. I'm not electroinc pro but I'm comfy with solder iron.

Thanks

alex_79 · May 12, 2012

I think you must leave the two pullup resistors (R212 and R208 in the schematic you posted), because TIA has "open collector" outputs. Anyway I'm not an expert as I wrote in the first post and I don't have the modded junior anymore so I can't help you very much to track down the problem.

SkalTura · November 28, 2012

I have a question.

I made the mod onto an external PCB with a socket, so the TIA chip is on the external board. Then I made a connector onto the origial PCB of the Atari. I connected all pins of the TIA to the original Atari board, exept the Lum0 - Lum1 - Lum2 - Color -Sync - Audio pins. Those pins go to my mod. (I made the mod from the picture on the first page, but with the 4050).

I think this is not the way though, because I don't see anythink on my TV...

I have the PAL 4 switch version, but it's different from the pictures I found on the web ??

I know this is a very old topic, but I guess a few of you have made a succesfull A/V mod ?

alex_79 · November 28, 2012

I connected all pins of the TIA to the original Atari board, exept the Lum0 - Lum1 - Lum2 - Color -Sync - Audio pins.

Those pins require pullup resistors (R29, R30, R31, R33, R34 and R35 in the PAL jr schematics): if the TIA isn't connected to those on the Atari, you'll have to add them on the external board.

SkalTura · November 29, 2012

Okay... I tried adding the pullup resistors, but now the screen is scrolling like crazy.

My Atari 4 switch version is different from yours. Mine doesn't have the 4050 chip (see pictures). Could it be that the pullup resistors in your Atari are different from the ones that I need ?

Also, even though I added the pullup resistor for the sound, I still don't hear anything.

Edited November 29, 2012 by SkalTura

alex_79 · November 29, 2012

Looking at the schematics by J. Sobola (here is his website, download the file "2600.zip" in the "SCHEMATY" section), the 4 switch model uses different values for the pullups, but I honestly don't know if that can affect the mod. I only have basic skills in electronics: I can use a multimeter, read a schematic and build a circuit but I can't design my own. I hope that someone more tech savvy here on the forums can help you to figure out what's wrong with the mod.

alex_79 · June 9, 2013

Bump!

While I used the modded junior for spare parts, I kept the perfboard with the mod and today I decided to install it on a 6 switch console which will replace the 7800 I use for gaming. Using the schematics as reference I found where to make the connections to the atari board and it worked perfectly just like it did on the junior.

Schematics of the mod are on the first post of this thread.

The following picture shows where to pick the the signals on a 6 switch PAL rev. B board. I also have a rev. 1 board and they are in the same places. Different revisions of the board could have the components arranged differently, so check the board against the PAL schematics using a multimeter in that case.

Power (+5V) and GND are not shown.

Resistor marked with a red "X" need to be removed (I just desolder one side and lift them from the board)

They are R215, R223, R234, R224, R222.

I didn't removed the two transistors like I did on the junior but I didn't notice any interference.

Edited June 9, 2013 by alex_79

alex_79 · June 12, 2013

I finished arranging the wires in the 6-switch console.

Since the console I modded is an heavy sixer which is quite rare in PAL-land, I didn't want to drill or modify the case, so I routed a short cable out the existing rf hole and terminated it with an inline scart socket.

There's a switch to select between composite and s-video hot-glued inside so it can be operated through the channel switch hole.

I built a scart cable about 3 meter long, so I can keep the console near me and operate the switches while I'm playing. I used a 4-pole mini coax cable to allow for composite, s-video and stereo audio signals (albeit the console has mono audio out, because the 2 audio channels are joined inside the PAL TIA). Little labels on the connectors indicate the direction of the signals, since I didn't need a fully wired bidirectional SCART cable for this application. I also have a cheap adaptor to use rca or mini-din cables in case I need to.

SkalTura · August 17, 2013

Question:

I have a Darth Vader PAL Atari 2600, and made a A/V mod to it, but I don't have any sound, an the picture is in black/white. The picture is perfect however, only no color...

Any idea what went wrong ?

SkalTura · August 21, 2013

Sound is working now... I had a faulty capacitor.

But still no color though.

Anyone ?

SkalTura · October 5, 2013

Finally got it working...

Look at the quality of the svideo signal, it almost perfect :thumbsup:

lodbro · December 15, 2014

Finally got it working...

Look at the quality of the svideo signal, it almost perfect

can you please tell med what you did to get colour?

i have a mod board from electronic sentementalities that i have modified to fit my 4-switch 2600.

i also get very clear picture and sound but the picture is in black and white...

SkalTura · December 28, 2014

can you please tell med what you did to get colour?

i have a mod board from electronic sentementalities that i have modified to fit my 4-switch 2600.

i also get very clear picture and sound but the picture is in black and white...

I took out the Atari chip added a socket. Then I made the mod on a board with pins that go into the socket, and a socket for the Atari chip.

In this way, you can always take out the mod and make the Atari original again...

At first I didn't get sound, and there was no color.

So I added a FMS6400 Dual Channel Video Drivers chip to the original schematic.

Now everything is working perfectly.

I have a small LCD TV in my workshop with an S-Video input. That gives me perfect picture.

When I connect it to the LCD we have in the livingroom, using a S-Video to Scart converter, the picture is a bit blurry.

I have 3 more of the FMS6400 chips.

If you can't find it on eBay or in your local electronics shop, let me know...

Edited December 28, 2014 by SkalTura

Quon · September 14, 2018

Hi... I know this is an old post, so sorry for necroposting. I just wanted to say thank you to alex_79 and everyone else involved in developing this mod, as I followed it for my PAL 2600jr to add S-Video and Composite to it, and I really appreciate all the work put into it, the well made schematics and the included pinout for the varying TIA chips.

I went with a small board with everything on it in order as presented on the initial schematic basically, with the composite mod in between the Chroma and the Audio parts, I also added a second capacitor to make a second audio line, as the TV is stereo, and if you just join the 2 together, it can affect the quality of the sound of other consoles that do have stereo sound on some TVs, like if you got left and right and just joined them together... it was just placing 2 capacitors with their positive sides connected to the audio source, and the negative going one to left, and one to right, as seeing as the capacitors have a polarity, they won't affect other consoles.

The figuring out getting all the components on the board in a good fit was a little bit of a headache, especially as I had to wait a while for 2 of the resistors to arrive so i couldn't finish what I started right away, but today I removed the original composite mod I had and replaced it with this new board, and started with hooking up just the composite part to see it that was ok, as I knew that worked, and got the same "quality" of picture I had before.

Once that was verified, I simply connected all the S-Video connections to get that part working, and it's not easy to solder with fingers crossed that you didn't mess something up on the circuit!!

I had originally gone with the 9 pin miniDIN connector the Mega Drive II uses as my output port, with the audio and composite wired up the same as the Sega console is so i could use those composite RCA cables if I wanted to, and just repurposed 2 of the RGB lines for Luma and Chroma, so this way I only had one cable going to the TV with full S-Video, rather than using the usual 4 pin S-Video connector and a separate audio cable.

I made my own SCART lead with the 9 pin connector on one side, and the SCART connector on the other, and added a little switch to the connector itself to change between Composite and S-Video, seeing as Luma and Composite share the same line inside the SCART plug, that way they won't be both using the pin at the same time. I made the cable a little shorter too to help reduce any interference and added resistance from length.

The results on my TV of the S-Video image simply blew the composite signal out of the water!! The image is crisp and clear, although in some games there is a strange colour ghosting where there seems to be like a red shadow next to the game image, and a green one next to that, it might just need a small adjustment somewhere, but apart from that it looks absolutely perfect on my modern TV, making the gaming experience a true pleasure compared to how it was with the blurry composite or the simply awful RF image.

... and this is why I am writing this, to once again, say thank you to the OP and everyone else involved, your work is truely appreciated and now, thoroughly enjoyed!!

Edited September 14, 2018 by Quon

alex_79 · September 14, 2018

I appreciate the appreciation, thanks!

And thanks for posting pics of your mod. That's really well put together, I wish I could do such a nice and clean job! (there's a reason why I didn't posted pictures of my finished mod... )
I like the use of the mini-din connector for all the audio and video signals (especially on the jr, where space is very limited). And, it seems that you also replaced the 3.5mm audio jack with a barrel connector for power. That's a good idea!

Quon · September 14, 2018

Hhehehe yeah, ummm... the power jack was because of a power brick issue, which I couldn't find a 2600 replacement without paying a stupid amount of money, but seeing as the Mega Drive/Master System ones are compatible powerwise, and in fact, most consoles of the time have the same power requirements and are compatible amongst themselves, and it was easier to get a Mega Drive one, I just changed the connector, as I've never much cared for audio style jacks for power anyway.

Another mod I added which you can't see is a front 9 pin joystick connector hidden under the the lip of the console, a bit like how the 5200 and 7800 had theirs, but this port is connected to just the direction, action buttons and ground of the left controller. The other 3 pins I intend to connect to the action button, up and down of the second joystick port, so when I make my arcade stick, I can plug it in to this front port and have 4 action buttons for Stargate (Defender II), and the frontal port still be compatible with the standard Atari joystick at the same time, and still have the back ports for things like paddles.

The 9 pin miniDIN, well, I ordered one for my Master System II for the RGB mod, and it came in a bag of 5... so, seeing as I had 4 left over, I thought I might as well put some good use to them hehehehe

I still need to finish the console off, like put the RF shield back on although I'm going to need to dremel that a bit to accommodate a couple of thing like the whole video mod, I've already done a complete recap of the entire console, which is only like 5 capacitors anyway, changed the 7805 power regulator for a switching one which runs very well, doesn't heat up and uses less power (the original regulator was running very sorry for itself), and changed the power LED to blue because, "why not"?

Next mod for this console will be the 4 button arcade stick, and I may make a Q*Bert arcade stick with the stick turned 45º, I'm not sure yet, I want to make an arcade stick for the Master System II before that, and I think that's about it for the moment, time to get back on track collecting games!!

CYA!! ^.^

Edited September 14, 2018 by Quon

alex_79 · September 14, 2018

The original jack briefly shorts the power supply to ground each time you insert or remove the plug, so that's another good reason to replace it.

Another mod I added which you can't see is a front 9 pin joystick connector hidden under the the lip of the console, a bit like how the 5200 and 7800 had theirs, but this port is connected to just the direction, action buttons and ground of the left controller. The other 3 pins I intend to connect to the action button, up and down of the second joystick port, so when I make my arcade stick, I can plug it in to this front port and have 4 action buttons for Stargate (Defender II), and the frontal port still be compatible with the standard Atari joystick at the same time, and still have the back ports for things like paddles.

Very clever! Stargate is one of the games I had as a kid, but actually I never used the second joystick: I only had two proline joysticks at the time and you can't easily press the button or move the stick on those unless you keep them in your hand...

Quon · September 14, 2018

Yeah, I had Stargate when I was little, and I really enjoyed the game, but I was gifted it as a cartridge only and I never knew anything about the controls from the second controller. Recollecting for the console, Stargate is in my list of need to get games, but I was looking into how much people like to get into the game, with making things like foot controllers with 3 large buttons to plug into the second port, and things like that. I like mods to be original and curious, but aesthetically pleasing too and without breaking too much of the general design, so I decided seeing as I was going to make a nice clicky arcade joystick anyway, I might as well make a "special Stargate port" for it on the console, although I think there are a couple of other games that can make use of this feature as they used the second joystick for things also. I like consoles personalised, but not obnoxiously so, like the blue power LED, which makes it stand out as my console, but it's not something that you see until you turn it on, and even then it's subtle.

I like how the controller port mod came out, as it's quite well hidden, but if you see it, it doesn't look out of place like a wart simply added on.

Edited September 14, 2018 by Quon

alex_79 · September 14, 2018

Yeah, I had Stargate when I was little, and I really enjoyed the game, but I was gifted it as a cartridge only and I never knew anything about the controls from the second controller.

I had the manual, but it was in english only and I couldn't understand a word of it at the time (I'm only slightly better now...). I discovered the extra functions by chance, when my cousin pressed the button of the second joystick while I was playing...

I like how the controller port mod came out, as it's quite well hidden, but if you see it, it doesn't look out of place like a wart simply added on.

I agree, it looks like it has always been there. Good job!

Quon · September 14, 2018

The internet has become a great tool for those of us that end up getting cartridge only games, as we can find most instructions online now. And when it comes to Atari 2600 games this is especially good with things like the difficulty switches on the back and their function, because it's not something that is "A is easy, B is hard" or anything like that, and often it doesn't even control the difficulty. I remember when i discovered Moon Patrol had background music controlled by a difficulty switch by chance, I was like "this game has music?? WOW!!" :-D :-D :-D :-D

gtremblay · July 12, 2020

Thank you!

With the TIA schematic for PAL and NTSC, I figure it out what to use for NTSC here in America to get the right colors

I resume what I do in this post :

thanks

pcrock · October 20, 2020

Hi @alex_79
Sorry for rebirth an old post but please let me know..
You tell that used the https://atariage.com/2600/faq/index.html?SystemID=2600#composite (4050 schematic) for build your project.
My question is.
On the real console there are already several components to make the Lum 0, Lum1, Lum2, Color and Sync lines up to the RF MODULATOR´s input.

Should I leave those components as they are or should I remove them from the Atari board?
If I leave them as they are, won't they interfere with the signal from pins 2, 5, 7 and 8 of the TIA CHIP that I will use for the new 4050 MOD circuit I am building?
Thank you friend.

alex_79 · October 23, 2020

I don't know for sure.

Since I used the cd4050 that was already installed on the board (this is only possible on 6 switch and junior models), I removed a few components to isolate the chip from the rest of the circuit on the Atari board.
But if you're building the full mod with an external cd4050 like shown in the FAQ, maybe the existing circuit won't interfere and you don't need to isolate it.

Sorry for the late reply, I didn't log in the forums in the past few days.

pcrock · October 26, 2020

On 10/23/2020 at 3:41 PM, alex_79 said:

I don't know for sure.

Since I used the cd4050 that was already installed on the board (this is only possible on 6 switch and junior models), I removed a few components to isolate the chip from the rest of the circuit on the Atari board.
But if you're building the full mod with an external cd4050 like shown in the FAQ, maybe the existing circuit won't interfere and you don't need to isolate it.

Sorry for the late reply, I didn't log in the forums in the past few days.

Thanks a lot friend. I did the 4050 mod and removed only the sound oscilator (transistor, inductor and the resistor that is the way to mix the signal to video).
I build two ones. Used 74HC4050. The results was GREAT!!!! My consoles are NTSC versions. Tried a lot lot lot of simple av mod versions, (with 0, 1, 2 and 3 transistors) but all of then was terrible.
The only one that gave me a CLEAN and PERFECT SCREEN with NO INTERFERENCES and NO NOISY PICTURES is even the 74HC4050 MOD

.