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

[Michael Rowen]

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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