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Date Posted: 19:20:58 12/17/01 Mon
Author: lcs
Subject: Re: Bad picture in Canton 4.2
In reply to: Jain 's message, "Re: Washed out picture." on 13:31:12 12/16/01 Sun


>Could we have the schematic of your amplifier?


I built several, using negative feedback from the
colector of the last transistor to the base of
the first one. It's not difficult to calculate
if you use Canton's design as a starting point.

I got a sharper picture and better contrast with
my amp, but there is an interference source that
causes dark horizontal stripes in the picture,
moving along with subtittles, peoples' lips,
heads, etc. It causes different brightness areas
in the picture and it's really annoying. At first
I thought this was a symptom of low bandwidth
in the video amp stage, but it wasn't.

I ruled out the video amp, burst signal and sync pulse.
Also modified the DC clamp level adjust and even tried
a direct connection to rule out the elect. capacitor
at the output. Also changed the video source, the power
supply, the TV monitor, the cable signal, etc. etc. etc...

I will have to modify the entire switch & video-out
circuitry, from the 4066 onwards. This is going to take
some time. Also discovered that the comparitor circuit
exerts some influence on the burst and contrast of the
picture, but not enough to cause this problem. My last
guess is, maybe I'm getting crosstalk from the 20Mhz
oscilator at the PIC.

lcs

PS.: I apologize to Juan Canton, but these problems
are making me pluck out the hair!! I was going to
build Canton 5 but decide not to, not yet.

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