[Coco] Coco 2 RF

Tue Feb 21 10:56:04 EST 2012

I'm intending to build and test this circuit on a CoCo 2 this weekend. I'll
post my results here to let you know if/how it works.

Cheers,
-Mike

---------- Forwarded message ----------
From: Mark Ormond <markormond at mtxsystems.com>
Date: Tue, Feb 21, 2012 at 7:56 AM
Subject: Re: [Coco] Coco 2 RF
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>

I copied the board layout of one I have in mine. The copied schematic is
currently untested.
Why don't you try it and let me know if there are errors.
I can post pics of the original board also.

http://www.svfdtn.com/cbm/coco2comp.jpg

 GND = GND

 G = Pin 8 of MC1372P

 Y = Y on Modulator

 S = S on Modulator

 R = Left side of C32 (Looking from front)

 Later,

 dabone

-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] On
Behalf Of haywire666 at aol.com
Sent: Tuesday, February 14, 2012 10:53 PM
To: coco at maltedmedia.com
Subject: Re: [Coco] Coco 2 RF

All this talk about coco2 rf reminded me... I have 3 coco 2's I never or
rarely use because the rf is pretty bad.

Dosn't someone have a circuit for coco2 (someone shared one on
coco3.combut it only works on coco1)
To produce video and audio signals? I'd like to mod my coco2's with a
couple of rca jacks in the back with
audio and video outputs if possible...

Steven

-----Original Message-----
From: gene heskett <gheskett at wdtv.com>
To: coco <coco at maltedmedia.com>
Sent: Tue, Feb 14, 2012 7:30 pm
Subject: Re: [Coco] Coco 2 RF

On Tuesday, February 14, 2012 07:02:53 PM Jeremy Michea did opine:

> â€œAs for your problem, I have never seen it, but since I am a CET, my
> best guess would be a dried out capacitor in your coco's video
> circuitry, causing the modulation to be much less than the 90% or so it
> was designed for, which in turn gives a very low contrast, and likely
> hard to sync to, image on a tv.â€‌
>
> Thanks Gene. That was kind of what I was looking for. I guess I still
> wasnâ€™t wording the question properly as some assumed I didnâ€™t know
> if Composite was simply better. It was more of wondering if it was
> simply a matter of the poor RF or if there was a deeper issue. For the
> record, Iâ€™m more than aware that composite is better quality than RF.
> I didnâ€™t fall off the coco turnip truck yesterday
>
> Sadly though I donâ€™t have an oscilloscope. Assuming the problem is the
> one you describe would it simply be a matter of desoldering the old
> capacitor and soldering in a new one? Unfortunately I donâ€™t have the
> soldering skills. Iâ€™ve never done it before although I have been
> wanting to learn, just not enough hours in the day at the moment.
> Thanks Gene for the answer though I appreciate it.

You could just form the leads of a somewhere near the same sized
cap(acitor), and paying attention to the polarity markings on both, connect
the test cap across the likely suspect and check the tv to see if it helps.
Don't be surprised if it still helps after the test cap has been removed.
What has happened in that event is the that the charging currents from one
cap to the other, have caused a momentary nano-weld between the foil of the
suspected cap and its lead where they are connected internally.  It won't
last long, sometimes only minutes, but that is the response that nails that
particular perp to the guilty list.

Bear in mind also that safe to use around electronics type soldering tools
are not the shacks strongest suites, it s/b temperature controlled (most
get several hundred degrees too hot if left turned on for 20 minutes) and
should have a 3 wire line cord, claiming a static grounded tip.  My fav
iron is sold by GC and their ilk for around $150 these days, and has a
meter reading in real temps as measured by a platinum sensor touching the
back end of the tip insert, and a dial knob to set the temp with, which it
will then hold within 10F or thereabouts.  It isn't the greatest iron, but
I've had it for going on 25 years and it still works great after probably
10,000 hours of on time.  It, or duplicates of it, have earned me close to
a million spread over the last 30 years while I was keeping a tv station on
the air.

When tracing the schematic looking for likely suspects, keep in mind that
the cap(s) I am thinking of would be somewhere in the path that could
effect the rf output, but not the composite, so that should narrow the
search to just 4 or 5 of the 80 or so caps in a coco.  Further narrowing by
eliminating anything that is not an electrolytic type should get you down
to 2 at most, and likely only one.

HTH, Jeremy.

Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene>
Kafka's Law:
       In the fight between you and the world, back the world.
               -- Franz Kafka, "RS's 1974 Expectation of Days"

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