[Coco] Strange video issue

[Salvador Garcia]

Congrats! Great to hear the news.


Uh... when you say "hot CoCo1"  hope you are not referring to its operating temperature ;-).


Salvador




-----Original Message-----
From: Barry Nelson <barry.nelson at amobiledevice.com>
To: coco <coco at maltedmedia.com>
Sent: Wed, Sep 9, 2015 7:54 pm
Subject: Re: [Coco] Strange video issue


I got it working properly! I made the following modifications. First, instead of
using pin 12 of U12 (MC1372) for the input I now use pin 1 of the RF modulator.
I also added a 10k pot and connected the input to one side, grounded the other
side, and connected the center to the first transistor's base lead. I also added
a 100 ohm resistor from the output end of the 22 ohm resistor to ground. It now
works great! I was able to fine tune the video using the pot, and compare it to
the TV output which also still works. I have reassembled the computer with the
new video and output jacks permanently installed in the back of the case. When I
have time I will post updated schematics to https://hackaday.io/. I have one hot
CoCo1 one now! 64K of ram, floppy controller, double sided floppy drive and
composite video mod working! Woo woo!


On Sep 7, 2015, at 11:44 PM,
coco-request at maltedmedia.com wrote:

> Date: Mon, 7 Sep 2015 20:29:59 -0500
>
From: Zippster <zippster278 at gmail.com>
> To: CoCoList for Color Computer
Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] Strange video issue
>
Message-ID: <3C0E0231-0771-4A40-8485-8F1DCA3E86A1 at gmail.com>
> Content-Type:
text/plain; charset=utf-8
> 
> Signal level/proportions are off.  That circuit
(Darlington pair with a decoupling cap) doesn’t allow for any adjustment.
> It
also may not help that the CoCo 1 doesn’t have a color burst generation
circuit.
> 
> Redesign the circuit to allow for amplitude adjustment and
proportion of sync to active video?
> 
> Hard to get more specific without
putting a scope on it.  The way it’s coupled through a 22Ω resistor kind
> of
makes me wonder what kind of receiving circuitry they were expecting on the
other end...
> 
> Can you compensate with the tint controls on your TV?
> 
> -
Ed


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