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

[Al Hartman]

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-[ Al ]-

-----Original Message----- 
From: Zippster
Sent: Friday, October 03, 2014 10:34 AM
To: CoCoList for Color Computer Enthusiasts
Subject: Re: [Coco] video composite on korean coco 26-3134A

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
>>>
>>>
>>>
>>>
>>>
>>> --
>>> Coco mailing list
>>> Coco at maltedmedia.com
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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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>
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