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Channel F Composite Mod

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I tried to search for this but could not find anything. Is there a composite video mod for the Fairchild Channel F?

Does anyone know of a link that describes how to do this?

Thanks

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I was able to get a weak picture off a System I unit, if you check the schematic at the VESwiki you'll see that there's a VIDEO INPUT SHT. 2 signal in the RF circuit:

http://classicdev.org/images/3/31/FVE100_schematic_sheet_1of3.gif

 

Looking at sheet 2 you see that it's close to the LED:

http://classicdev.org/images/5/55/FVE100_schematic_sheet_2of3.png

(lower right corner)

 

http://classicdev.org/VES_Schematic

With help from the SABA Videoplay 2 schematic it should be possible to find a point to pic the composite video also, I'm guessing somewhere after the "chroma" and "burst" signals are put together from the video circuit...

 

I lifted the signal on my Luxor version, and was able to get a composite picture on a Commodore 1084S-II monitor, on a real TV it was very weak.

 

So I think it's simply a matter of amplifying it and perhaps disconnect the RF circuitry. Someone with a scope and knowledge of how a video signal is supposed to look is probably able to make a proper adjustment. You could tap into the speaker to get an audio output, just adjust the level with a adjustable resistance.

 

Here's where I picked up the signal

2Vs9MS.jpg

The original machine has a different layout, but you should be able to find the right place. It could be hidden under the shield as well though.

 

 

Very sharp picture but weak, I tested it on a unit I thought was broken, but I later noticed that a leg on one of the Video RAM circuits was bent.

2Vshgi.jpg

 

I also found out that the then current version of Pac-Man had too little delay in the graphics plotting routine, hence the blurry graphics here:

2VuYT0.jpg

I had to set the brightness knob to max.

 

To even get a picture on my TV I had to run it through the VHS-machine:

2VtN2J.jpg

 

I tried making a small amplifier circuit but had no luck with it (it's a little out of my area, I should brush up on video electronics I guess).

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EDIT: OK, here is my suggestion. You may be experiencing significant voltage drop across R54 and R56. Try clipping smaller resistors (or even pots) parallel to these and see if it brightens up.

Edited by batari

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The PAL board I hooked up isn't marked with any silkscreen or similar, and it differs a bit from the schematic (as that is for an original NTSC unit) so I kind of just poked around in the general area (General Area!) until I got a picture. It would be a very nice hack just to be able to add a resistor or two and get a normal picture.

 

I have a US-version, but since it's untouched and working I'm not going to open it up...

 

Oh, so it's the pulled up buffered Chroma and Burst signals from the '07 circuit in position E3 on the original board... I don't have a single '07 circuit on my board but I guess I can look for the resistors.

 

mTvvJ.jpg

 

I guess the 74LS153 located near the RF box is the one that outputs these. BTW there's also GREEN, BLUE and RED input on pins 3-5 of this, it would be really cool with an RGB output...

 

Here's a closeup:

81YLA.jpg

 

I'm pulling the signal from the 2k2 that's connected to the LED, should be R80, so the 470 and 180 Ohm resistors that are soldered into the same node is probably the R65 and R64. Yes, checked the 180 there is connected to pin 10 of the 7445 just below that row of resistors.

 

Checking furter on the 74LS153, where we get Chroma and Burst, it seems they are connected directly to the 1k5 and a 3k3 resistor instead, they're pulled to +5V 2k for Chroma and 3k8 for Burst... I'm guessing they could be different because of PAL video levels and color encoding perhaps.

I have checked some things and added text to the image, the FPN 2369 NPN that has it's collector connected to the video signal is not in the schematic.

 

ngK29.jpg

 

I'll try and adjust the Chroma and Burst resistors then...

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Putting 1k parallel with the 1k5 resistor at the Chroma signal boosted the colors a bit brighter, but the overall picture still has the same darkness. White level is still at the same brightness. Messing with the Burst signal resistor only made the color disappear. I don't think there's any idea messing with these, the colors get a little stronger but starts to bleed instead.

 

Actually unhooking the RF circuit from the video signal might help, I think I need to go under the RF sheld then and probably detach the bottom shield from the circuit board to get there.

 

 

Perhaps this would be enough, taking the composite video signal at the 10k resistor.

ataricct.jpg

http://www.r3uk.com/index.php/tech-tips/39-cool-projects/71-atari-2600-composite-video-mods

Some adjustements to the components may have to be done to increase or decrease the level.

 

I wish I had a scope to check out the signal...

Edited by e5frog

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I asked Ben Heckendorn, he suggested an amplifier circuit like the one above, that should be enough, then you can just pull the sound from one of the speaker lines and maybe adjust the level of that with a resistance. I could plug the signal right into my TV without any obvious problems though and get a proper audio level.

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I don't think the Channel F has a luma signal like the 2600 does, it's an 8 color machine isn't it? That is, the "luma" is either on or off. The D/A resistor ladder in the above circuit doesn't apply. At the very least, a Channel F circuit should be simpler than the one above.

 

There may be another way to do it without requiring an amplifier. I'll look at the schematic again.

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Well, I hooked it up like above, the composite signal going into the 10k resistor and amplification is pretty decent. The 20 Ohm resistor to 5V isn't really needed as far as I could see...

 

I used a 2N3904 instead though, problem for me is - I get no color - it could be a PAL-issue, I'm trying to figure it out, could also be the video levels that are off - I wish again that I had a scope to check it out.

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Well, I hooked it up like above, the composite signal going into the 10k resistor and amplification is pretty decent. The 20 Ohm resistor to 5V isn't really needed as far as I could see...

 

I used a 2N3904 instead though, problem for me is - I get no color - it could be a PAL-issue, I'm trying to figure it out, could also be the video levels that are off - I wish again that I had a scope to check it out.

Since you say a parallel resistor in the BURST circuit lost the colors and the amplifier does the same, it would stand to reason that BURST doesn't like being amplified.

 

If you're getting a reasonable brightness, that's good, but it sounds like you need to attenuate BURST before going into the circuit. You could clip R54 and replace with a larger value, or just grab BURST and CHROMA separately and make your own combining circuit with larger resistor on BURST.

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I decided to keep the original resistors on the Chroma and Burst signals - and (on my PAL unit) also the third signal (whatever it is) that is connected to the same node, the resistor to +5V in the was left there, I didn't see any difference with or without it when done.

 

After amplifying the now black and white picture i tied the color signal to the amplified signal and "voila" a pretty decent picture.

 

Disconnecting the RF circuitry may help even further, I'll see if it helps.

 

I haven't made any adjustment for the impedance, just a 10k, a 47k resistor and a 2N3904 transistor.

 

Amplified composite signal - no color:

aVs27x0.jpg

 

Needed circuit on a 5x5 hole continuous stripe kind experiment card, the unused one is for ground.

aVs2f0r.jpg

 

I needed to lift and re-tie these three resistors together to circumvent loosing the color:

aVs2hvA.jpg

 

This is how it could look when attached in the console:

aVs2cwi.jpg

 

Image when connected:

aVs2a19.jpg

 

 

I'll check if the signals are S-Video compatible.

 

 

Now, if someone could send me an American unit I could see what needs to be done there, I have been working with a PAL 100-E motherboard here, which of course differs slightly.

 

 

The sound can be lifted from the speaker amplifying circuit, easiest way is to disconnect one of the speaker wires and grab it there, a resistor may be needed to lower the level though I had no trouble connecting it directly to the TV.

 

So this way you could get a decent picture and sound on the TV even from an old unit like this.

 

A shielded 75 Ohm cable with a female RCA connector connected to it hanging out where the RF cable previously was should be enough, and one just like it for audio (but 50 Ohm, not that it makes much difference) and your 1976 console may just be ready for a modern TV. ;-)

Edited by e5frog

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I know this thread is quite old from 2010, but I wanted to ask e5frog if his description here is now the latest status, or if there were any imrovements made for the mod in the meantime? Reason I am asking is that I own a European PAL SABA Videoplay which needs to be modded and I want to start that project soon. ;)

Thanks!

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I didn't revisit the mod, but I know someone managed to make a working mod from this thread. I asked for details but didn't hear back. I have pretty good picture from my units so that's one reason I haven't done anything more about it.
SABA should be easier as there's schematics on veswiki.com for both SABA models.

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Thanks, I think that someone from the German circuit-board.de mentioned your mod but he didn´t tell then what exactly he did change on your mod in the end.

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I really need an S-video, composite or RGB mod for my Fairchild Channel F. Anyone have good schematics for a mod or know where I can get a kit?

 

Thanks in advance!

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In general it's a matter of isolating the composite signal from the RF part, then adjust the signal levels to work by itself.

You need enough amplitude but also starting at the proper level.

 

Don't know of any kits or finished instructions on how to do it.

 

Video could probably be improved by adding a video IC with filters etc but it should be possible to get a good result with one or two transistors and a few resistors.

 

I did mark some things up on a PAL board a while ago, not that you'll have much use of it.

Img_1480.jpg

I can only refer to the things already posted here and the schematics:

http://channelf.se/veswiki/index.php?title=Schematics

 

I think there's another thread here on this topic, I seem to recall posting the reverse engineered Bomarc schematics as well.

 

 

If you have the old version you should locate the composite signal where it says "VIDEO SHT 1" on this schematic:

http://channelf.se/veswiki/images/0/04/FVE_schematic_sheet_2_of_3.png

That's what goes into the RF circuitry and has all needed parts of the composite signal, just not the proper levels.

 

I think I got this from another guy trying to video mod (it will get bigger if you click it):

Bomarc_schematic_pieced_together.jpg

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FOUND IT!!

 

Here's the thread with the successful mod:

http://atariage.com/forums/topic/255438-fairchild-channel-f-model-1-av-mod-help/

 

I wouldn't call it successful.

I got too busy to keep working on it.

 

Looking at it again it should be as simple as lifting C20 one end would be Chroma and the hole would be Luma and Sync.

try that into series 75R if poor video try amping into a THSxxx or FMS6400

 

Let me mess around with this again real quick.

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Correction C28 is where Chroma and Luma are mixed. I got nothing when I messed with this but I think I may have fried something at some point.

I think with a fresh Channel F I could figure it out

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Posted (edited)

Hello,

 

It's a pity that the pictures and the explanations are so unclear... I don't understand much, but the MOD board has only 3 components.

Would it be possible to have a summary electrical diagram with the exact connections to be made on the console please?

 

The schematic proposed above has many more components and the connections to the console are not all explained

(for example, what is the light blue wire on the picture of the assembly?)

Edited by ppj34
precisions

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