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Date Posted: 19:42:58 01/12/03 Sun
Author: Phil Q.
Subject: Re: Canton 4.2 questions
In reply to: KidNovak 's message, "Re: Canton 4.2 questions" on 11:22:16 01/10/03 Fri

It's been a while since I built my 4.2 and modified the design and I'm fuzzy on the particulars so don't sue me...

If you're using this for a GI system and it uses line 18 info, make sure you are using Sakman's latest revision of the board, the info is on Canton's web site. There are a couple of components swapped that will keep it from decoding the info on line 18 (or whatever line your provider is using, some have moved it around).

Definitely do the Scenix mod.

You may also want to change the biasing on the final output transistor amplifier stage. I changed the transistor in mine from the 3904 to a 2N2222a because it has a wider linear operating range but you should be able to get decent results from the original transistor. I seem to recall that he didn't take the .65v drop across the junction into account when he did the biasing, so it is decidedly non-linear, clipping one side of the waveform a bit. The signal going into that final stage looked good though so that was the only problem. Although I was able to improve the output quite a bit I never did quite get it perfect but I didn't know as much about proper biasing back then. I'm sure you can get it right with a little work. There should be some messages archived somewhere where Sakman and I discussed some different resistor values in that stage and the results we were getting.

Finally, the colorburst gets mangled a bit in one of the stages, I was working on that problem when we dropped our cable and went to DirecTV... so I have no idea what to do about it but from the looks of it on the scope it looked like another biasing problem. The color looked pretty good though so my TV didn't appear to care very much.

- Phil


>Yes the CFT2254 is a GI box.
>According to my CFT2254 model number, it does not use
>audio privacy, TOCOM or SA.
>
>Since I already have a SX-Blitz programmer I will do
>the SX-20 mod.
>
>Do you know if I will have to make any hardware changes
>to Canton 4.2, if using the SX-20?
>
>I will be using this sx code "gisx20.asm", it says it
>works with canton 4.2.
>
>Your help is really appreciated.
>Novak

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