5508W AGC fix -- New 3C

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Date Posted: 10:03:12 08/26/01 Sun
Author: Potter
Subject: 5508W AGC fix

After reading all the posts regarding AGC problems I started looking for a solution for this box (5508W type 3) - thanks for the inspiration everyone!
Went through my schematic traces and the answer was right there in the box - a black level AGC sample & hold circuit based on a TL082 opamp and a 4066 which is driven by a dual monostable (4538). I'm driving this circuit from RA2 on the decoder (SX18) with a minor change to the software and it works perfectly. RA2 is connected to D205 to take advantage of the existing TTL to CMOS logic level converter.
A logic 1 on RA2 (to D205) takes a black level sample on 1 line/frame (modify makehline), 0 then uses the sample to shift AGC appropriately.
(Use their own weapons wherever possible)

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Replies:

Re: 5508W AGC fix -- Tom, 13:26:05 08/26/01 Sun
- Re: 5508W AGC fix -- Potter, 07:30:20 08/27/01 Mon
  - AGC fix Schematic -- Tom, 20:25:10 08/27/01 Mon
    - Re: AGC fix Schematic -- Jain, 19:11:36 11/27/01 Tue
      - Re: AGC fix Schematic -- Potter, 05:41:58 11/28/01 Wed
        Re: AGC fix Schematic -- Jain, 14:36:57 11/28/01 Wed
        Re: AGC fix Schematic -- Potter, 09:55:58 12/01/01 Sat
        Re: AGC fix Schematic -- Jain, 08:22:42 12/02/01 Sun
        Re: AGC fix Schematic -- Potter, 10:40:48 12/02/01 Sun
        Re: AGC fix Schematic -- Tom, 17:34:08 12/02/01 Sun
        This should be read by everyone atempting to build 3 chip -- Jain, 09:16:27 12/09/01 Sun
        Instability on scrambled channels -- Phil Q., 08:35:09 12/12/01 Wed
        Re: Instability on scrambled channels -- Jain, 18:36:54 12/12/01 Wed
        Re: Instability on scrambled channels -- vg, 14:52:00 12/13/01 Thu
        Re: Instability - test it first -- lcs, 20:03:22 12/13/01 Thu
        re: Instability -- Phil Q., 12:27:42 12/14/01 Fri
        Re: re: Instability -- lcs, 20:17:34 12/14/01 Fri
        Re: re: Instability -- Potter, 04:31:38 12/17/01 Mon
        Re: re: Instability - edge detectors mod. -- lcs, 22:00:33 12/27/01 Thu

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