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Fairchild V.E.S. / Channel F Composite video mod

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Studying the PCB-schematics for the FVE 100 as it is called on the schematics I noticed where the VIDEO input to the RF part was...

 

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VIDEO INPUT SHT 2 it says... so I looked at sheet 2 and find this:

 

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As you can see by the discreet arrow I added - there's a LED inside the unit by the RF-box, and after that there's a resistor where the VIDEO is connected to the RF-circuit, three resistors meet in that node, so although I don't have those coordinates along the edge of the PCB in my Luxor V.E.S I managed to find it pretty easy - no components at all are marked out by the way:

 

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I decided to try it using my defective spare unit connected to a C= 1084S-II monitor:

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Nice! But quite weak picture, trying it on my working unit there was no difference in quality really - I had to turn the picture very very bright - black is almost the same color as the background:

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When trying to connect it to a plain TV, I got no picture at all until I connected it via a VHS-machine, just putting the signal through - looks awful:

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I'd like some help to modify it so that I get a proper signal - the picture is excellent - well worth running on a big screen at the next "local" convention here in Sweden Retrogathering 2007 weekend October 6th (my birthday BTW).

 

But then I thought, why stop there - we might get RGB right away from here (yes it says BLUE in the middle):

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But there I'm certain I need some sort of amplifier - I know I've seen an RGB mod for another console where such an amplifier was built...

 

I'd like to get the best picture possible: RGB, S-Video (Y/C) or Composite

 

HELP.

 

 

Here are the complete schematics (it says there are supposed to be 3 sheets, but I only got 2). I am in the making of redrawn schematics without all that black dotty crap in the picture. It's nice to be able to understand why you have to do certain things while programming, using ports for controller input and such:

 

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I also noticed that the current build of Pac-man doesn't run on the old version of this console - the delay when plotting graphics need to be longer. It works fine in the second version of the unit, with the VLSI chip instead of all those TTL circuits, I'll see if I can make an RGB/S-Video/Composite mod for that as well, but unfortunately I have no schematics for that one...

 

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Thanks for your interest.

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First page done!

 

I'll give away free System Fairchild Luxor stuff to the first person who redraws the second page - it took quite a while!

 

I recommend printing it in poster mode 3x3 pages on yellow paper - and then frame it and hang on a free wall. ;-)

 

 

 

Went from a 2MB jpg to a 300kB gif... phew.

 

 

Many thanks to Jasc Paint Shop Pro 7 for starting (and closing) a lot faster than the competing Adobe product I won't mention by name. ;-)

 

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I don't know about Y/C or RGB, but for a stronger composite output you could remove the loading of the RF modulator by unsoldering the leads of L2 and C19 which connect together (this should be electrically the same point where you tapped into the composite signal for your output).

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I don't know about Y/C or RGB, but for a stronger composite output you could remove the loading of the RF modulator by unsoldering the leads of L2 and C19 which connect together (this should be electrically the same point where you tapped into the composite signal for your output).

 

 

... and these are probably under the metal shell next to the LED....

 

I was thinking if I need to correct the impedance (efter cutting the load of the RF-circuit), it's supposed to be 50 ohms, right?

Don't know how I go about that.

 

On the portable NES I'm building for a dear friend the French constructor tipped that a resistor had to be replaced with a 50 ohm resistor to get better picture when drawing composite video directly from the board after removing the RF modulator.

 

Yesterday I saw the exact same type of machine a NESp, in a wooden shell! Mine is built from the NES-shell, looks extremely NES-ish.

 

I might have to sit down and do some actual work on that, good that I found my Electric and electronics schoolbooks today... *sigh*

 

I might just emulate it in some program instead... any tips?

 

 

 

Fredric

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I mean it - go right ahead.

It would be nice to print out the second sheet as well and poster it on the wall.

I got all the components traced out, but now the text is taking forever. Not to mention I already did a significant portion of text without antialiasing, so the font is large and blocky : ( Hope that's okay.

 

Also, the scan destroyed some of the component labels. Do you have the original sheets? I may need to ask for a couple numbers later when I get to those parts.

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I mean it - go right ahead.

It would be nice to print out the second sheet as well and poster it on the wall.

I got all the components traced out, but now the text is taking forever. Not to mention I already did a significant portion of text without antialiasing, so the font is large and blocky : ( Hope that's okay.

 

Also, the scan destroyed some of the component labels. Do you have the original sheets? I may need to ask for a couple numbers later when I get to those parts.

 

 

Nope - don't have the original sheets...

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I still need help in perfecting the mod, maybe I'll remove the RF-shield and see if I can find isolate a better point to tap the composite video.

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I bought a SABA Videplay 2 with half a composite mod, image was weak and all graphics was kind of purple-ish.

I managed to balance the transistor hookup and improve the image, gives a near perfect image on two CRT:s and an LCD TV although the signal amplitude is about half of what it should be.

It looks as if there's a possibility to get s-video from it, color sneaks through the Luma-signal but it can be filtered out and used as luma+sync and then have burst+color on a separate hookup.
The FMS6400 used in the Longhorn s-video/ composite mod for the Atari 2600 seems like a good candidate for cleaning up the signal and get proper output - as soon as I clear the workbench...

Audio was picked from speaker line and a resistor added to get about 0.9Vp-p, as consumer audio line in usually is (audio was pretty much the same level as when using RF).



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Was that the butchered up unit you bought from Kralleman? Good to hear it wasn't DOA from the previous modder's attempts to get composite video.

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Yes, that's it Carlsson, it worked fine on RF with mod removed, after reseating chips. I spent a good hour measuring various signals and swapping chips without finding anything wrong. With all original chips back in place it came to life. Image was just a mess in grayscales before that. The "graphics" chip was ceramic with gold pins, that wears the socket a bit extra over time.

With mod back in I got a weak image and started balancing the signal imperically with the oscilloscope as visual aid.

Came out pretty well with just a transistor and resistors (had to lift one pin of a resistor on the board as well) but only about half the proper amplitude.

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The FMS6400 will do a good job, but just a heads up its pretty finicky about the input signal voltage levels so have those sorted, and out of the box the outputs are setup for a 150ohm load and it will work fine on 75ohm lines, but it gets kind of warm doing it, somewhere in the data sheet it shows 75ohms going from the output lines to ground to drive a 75 ohm load

 

good luck

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Aha, maybe I should adjust the peak voltage then.
The Atari 2600 Longhorn mod has 75 Ohm to ground on the output and also 75 Ohm in serial after that before the output - but it's using the 6dB channel gain so I guess that's the explanation for that.

If it needs 1Vp-p on Chroma in I guess that needs a separate amplifier.

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