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Date Posted: 19:11:36 11/27/01 Tue
Author: Jain
Subject: Re: AGC fix Schematic
In reply to: Tom 's message, "AGC fix Schematic" on 20:25:10 08/27/01 Mon

Hi everybody
Here is a long story... I'll jump some stages... In Toronto there are scrambled chanels (still) available from Rogers. I build (years ago) the 9 (10, eventualy 12) chips discrambler... it worked, I improved it... A work mate designed a different kind of discrambler, with only 2 (two, a LM 319 and a 74LS123) chips, works fine, but is a hell to make it work (and it doesn't do a good job on unscrambled channels). Time before I had a chance to take a look at a 3 chips descrambler in a Samsung cable adapter (put there not by Samsung but by someone in SE Asia); the owner complained that it didn't work as it used to... I manage to improve it's behavior by increasing the input video level (the module was in resin, no way to dig in), but something was wrong inside, it was running very hot. My mind remained at that module. 2 years later I found the schematic on the net (the original 3 chip, with mpsa64). But I didn't build it. Until two month ago, when I found (in a flea-market) a... Samsung cable adapter with the label 'NEEDS WORK, $5' (canadians). I bought it and I found inside what I expected... in resin. But there it was another cable adapter (no, not Samsung), with the same kind of label and I bought this one too... there it was no resin, just the discrambler. I reverse engineered the module: 3 chips with mpsa64. But it had a 7808 as a regulator (!!!)... It had other problems too. So, I said I could try to build this circuit, and I tried to find again the schematic. So I found this place, I read messages (all), I found 'The information page', Canton's page. Some things are still not clear (not only to me, I guess).
Here, the scrambling system is with supressed Hsynchro, no audio scrambling, no video inversion, no burst gamming, Vsynchro normal. I understand that in this case Canton 3 and Rev7t1a would do the job. Actually, it doesn't (I do not know why, I'm still trying to figure out). The circuit works fine (I followed the Troubleshooting Guide). On some unscarmbled channels locks OK, on other no. On some scrambled channels locks OK, on other no. I had the posibility to change the input level, but it didn't help much (code in a c54jw). I should mention that is not exactly Canton 3, but Dave's 3 chips (no adjustments for Input and Output level). I'm willing to try the real Canton 3, or even Canton 5 --if it is appropriate, nobody says it'll work or not on the (simple) scrambling system I'm dealing with here (I sow the circuit for AGC in the message below, I'm willing to try it too). But my skills in programming are poor, so I cannot do a full job. I intend to try (for convenience) the circuits on a predrilled board with SMT's (where possible). I have f84a, c54jw, programer for both.
Problems: what was wrong with my first attempt (I hev a digital scope, I sow the waveforms, they look OK, but the lock is in the wrong place, sometimes both for vertical and horizontal...
Someone to tell me that (a simplified) Canton 5 will work on this scramblig system...
And.. who can give me (and when) a code for Canton 5 to test?...
I hope for some answers to this very long post.
J

>Here's the schematic of Potter's 5508W AGC fix that
>may apply to most 3chip installations to fix AGC
>problems. I changed some parts so it would interface
>directly to the PIC and use +5v supply. If anyone is
>feeling ambitious, they can give it a try. You will
>need to modify the code to use a unused port from the
>PIC to sample the AGC during the VBI or first few
>lines of video.
>
>

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