[Coco] video composite on korean coco 26-3134A

Fri Oct 3 10:34:55 EDT 2014

Hey guys,

You may have missed my earlier post.  I did a version of this circuit in Eagle.
Sound output is included.

The files are in the zip on this page.  CoCo2 Projects (Tandy Color Computer 2) - The Zippster Zone

I put it up as a shared project on OSHPark.  OSH Park ~ Coco2 Composite Out (Type 01) Rev 03

I laid the board out to replace the RF modulator in my Korean CoCo2’s, but as long as you get
the signals to it, you could mount it anywhere.

-Ed

On Oct 3, 2014, at 7:20 AM, Michael Rowen <mike at borncoco.com> wrote:

> John is indeed correct. I have built the simple circuit that includes a 1372 that connects to the signal from the 6847. It works well on every monitor I've used with a CoCo 2. The circuit is in the data sheet for the 6847. I have not had the time to create a PCB with Eagle. Some CoCos have the 6847 socketed, so it would be easy to make a board that plugs into that 40 pin socket, with the 6847 plugging into the board. CoCo 2s with a soldered 6847, would require 7-8 clip leads, but can be done. I have bread boarded this on a CoCo 2. This was the same method used by the Colorware adapter. I scored one of these at last year's CoCo fest. Its circuit uses more caps, but the principle is the same. I have not found any significant quality differences using the reference circuit. Clean and sharp. Any Eagle experts with some time on their hands to create the PCB files?? :) It will probably be Christmas time before I get the chunk of time to tackle this. I'm a newbie with Eaglecad. I'll try to post a video this weekend.
> 
> Cheers,
> Mike Rowen
> 
> 
> 
> 
> 
> 
> 
> "John W. Linville" <linville at tuxdriver.com> wrote:
> 
>> NTSC CoCo2's use a modulator that does _not_ take a composite video
>> input.
>> 
>> The 6847 outputs signals called Y, phiA, and phiB.  These are (very)
>> roughly analogous to the YIQ signals that form a composite video signal.
>> A Motorola 1372 chip is used to combine those signals into something
>> useful.  The 1372 chip can produce either a baseband composite video
>> signal or (by use of an RF tank circuit) a TV-compatible radio signal.
>> 
>> On the Coco1, the 1372 only produced a composite video signal that
>> was then fed (along with the audio signal) to an off the shelf RF
>> modulator.  On the CoCo2, the 1372 chip is only included as part of
>> the RF modulator itself.  The Y, phiA, and phiB signals go straight to
>> the modulator where the RF-equipped 1372 turns them into a TV signal.
>> 
>> I'm not sure if there is a pristine composite video signal available
>> anywhere inside the RF modulator on a CoCo2.  I was never able to
>> find one, FWIW.  You probably need to pull the modulator and build
>> a new 1372-based circuit to replace it.
>> 
>> Good luck!
>> 
>> John
>> 
>> P.S.  It sounds like the PAL CoCo2 might be designed more like the
>> CoCo1 in this regard.  Of course, that only helps you if you are
>> using a PAL CoCo2... :-)
>> 
>> On Thu, Oct 02, 2014 at 09:56:31PM +0200, didier derny wrote:
>>> Hi,
>>> 
>>> I tried but no success...
>>> 
>>> I don’t have any image on tv (connected to the antenna)
>>> No idea if the coco 2 is broken or if my tv is unable to process the signal
>>> 
>>> With the oscilloscope I've not been a able to find a composite signal 
>>> Inside the modulator...
>>> 
>>> Any idea ?
>>> 
>>> Thanks
>>> 
>>> 
>>> --
>>> didier
>>> 
>>> -----Message d'origine-----
>>> De : Coco [mailto:coco-bounces at maltedmedia.com] De la part de Simon Jonassen
>>> Envoyé : samedi 27 septembre 2014 16:26
>>> À : 'CoCoList for Color Computer Enthusiasts'
>>> Objet : Re: [Coco] video composite on korean coco 26-3134A
>>> 
>>> Hey....
>>> 
>>> I did mine by tapping into the feeds that go directly to the rf
>>> modulator....
>>> 
>>> A couple of shielded wires soldered on to the pins and 2 rca jacks on the
>>> rear of the case (audio/video)
>>> 
>>> Works fine... No extra components needed (PAL machine)... 
>>> 
>>> /Simon :-)
>>> 
>>> 
>>> -----Oprindelig meddelelse-----
>>> Fra: Coco [mailto:coco-bounces at maltedmedia.com] På vegne af didier derny
>>> Sendt: 27. september 2014 13:23
>>> Til: 'CoCoList for Color Computer Enthusiasts'
>>> Emne: [Coco] video composite on korean coco 26-3134A
>>> 
>>> Hi
>>> 
>>> Is there an easy way to get a video composite signal on this machine ?
>>> 
>>> I guess a video composite signal or something approaching should be found
>>> Somewhere near the modulator or inside the modulator ?
>>> 
>>> 
>>> Thanks
>>> 
>>> 
>>> 
>>> 
>>> 
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>>> 
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>> 
>> -- 
>> John W. Linville		Someday the world will need a hero, and you
>> linville at tuxdriver.com			might be all we have.  Be ready.
>> 
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