[Coco]  Re: New CoCo 3 - RF Out problem

Gene Heskett gheskett at wdtv.com
Sun Oct 25 21:44:14 EDT 2015


On Sunday 25 October 2015 20:40:51 Zippster wrote:

> Hi Chad,
>
> As Rogelio was saying, check the 8v supply to the RF.
>
> The fact that composite out is working tells me that the Q3 EF circuit
> is working. The output is split off right after that to both the RF
> box and another EF to the composite out jack.
>
> The output from Q3 is AC coupled via C67 into the RF box.  I’d check
> to make sure that cap (an electrolytic) is good, and that the video
> signal is making it into the box. The only things I see in the
> modulator that might have gone bad are a couple of small
> electrolytics, and a couple of transistors(less likely).
>
All of those "small electrolytic's" are to be considered highly suspect 
with the amount of time on them by now.

> Do you have a scope?  Definitely entering territory where one would
> help here.

Yes, the only way to see a definitive answer.

Those that are 'bypass' should not have any noise on either terminal IF 
they are still doing their intended job, just the DC voltage level 
differences.  That C67 coupling capacitor should have good video on both 
ends, but with a DC voltage offset.  If it has tilted lines of video on 
one end, its toast.
> - Ed
>
> > On Oct 25, 2015, at 6:46 PM, chadbh74 <chadbh74 at hotmail.com> wrote:
> >
> >   It's a 26-3334
> >
> >   -Chad
> >
> >   https://sites.google.com/site/cbhlab101/
> >
> >   Sent from my Galaxy S4
> >
> >   --------- Original Message ---------
> >   From: Al Hartman
> >   To: CoCoList for Color Computer Enthusiasts
> >   Date: Sun Oct 25 18:26:52 CDT 2015
> >   Subject: Re: [Coco] New CoCo 3 - RF Out problem
> >   What's the catalog number on the unit?
> >   Could it be a PAL Coco 3?
> >   -[ Al ]-
> >   -----Original Message-----
> >   From: Chad H
> >   Sent: Sunday, October 25, 2015 6:23 PM
> >   To: 'CoCoList for Color Computer Enthusiasts'
> >   Subject: [Coco] New CoCo 3 - RF Out problem
> >   I FINALLY acquired a CoCo 3 that was in uncertain condition. He
> > said the
> >   last time it was used years ago it worked fine though. It was
> > still sealed
> >   appears to be the base 128K setup. The first thing I did was
> > switch my RF
> >   cable from my CoCo 2 to the CoCo 3 and power up...click but
> > nothing else. I
> >   pressed the RESET button and could hear the relay click, but snowy
> >   picture
> >   on the old TV. Switched the RF 3/4 switch a few times and nothing.
> > Put the
> >   cable back to the CoCo 2 and its perfect image again.
> >   I then took the unit to another TV that had a front hookup for RCA
> > Line IN
> >   and hooked it up that way. The expected startup message comes
> > right up, nice and clean.
> >   Anyone have idea what could be going on here? Simple fix I hope. I
> >   could
> >   still use it in Line IN mode but I would rather have the CoCo
> > FULLY functional if possible.
> >   - Chad H
> >   http://sites.google.com/site/cbhlab101/
> >   --
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> >
> > --
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>


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