Re: DTV questions

From: Daniel Kahlin (
Date: 2005-11-26 16:33:52

On Sat, 26 Nov 2005, Ullrich von Bassewitz wrote:

> On Fri, Nov 25, 2005 at 10:51:52AM -0500, Golan Klinger wrote:
>> Does your unit suffer from the colour problems being described in
>> comp.sys.cbm and on the DTV hacking message board? People seem quite
>> agitated over the problem.

>  * The resistor arrays used to mix chroma and luma bits have different
>    values. I cannot currently tell which one is which, but one uses 2K/1K as
>    in the schematics, the other uses 680/330.

Luma uses 680/330.
Luma0 -> R14
Luma1 -> R18
Luma2 -> R22
Luma3 -> R12 or R26
Sync  -> R26 or R12

Chroma0 -> R15
Chroma1 -> R19
Chroma2 -> R23
Chroma3 -> R27

>  * Even more important: The active output mixer/buffer stage (Q2) is
>    completely missing. The output using the 2K/1K array goes almost straight
>    to the video output, while the one that uses the 680/330 array is sent
>    via a low pass/band pass filter similar to the one in the schematics to
>    the video jack.
> The next step should be to identify the chroma and lumina outputs. Once this
> is known, one could replace the existing circuit by an active mixer/buffer as
> it is shown in the schematics and check if this fixes the color issue.
> Unfortunately, I'm not brave enough to remove the die cover. Does anybody know
> how to do this without destroying the chip?

I was brave enough to look a my photo and think. ;)
Quite funny that we came to a similar conclusion at the same time! :)

Look here for my findings and a great shot of the video mixer:

/Daniel Kahlin

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