Re: VIC-II and luma levels

From: Gerrit Heitsch <>
Date: Fri, 13 Jan 2012 18:45:09 +0100
Message-ID: <>
On 01/13/2012 06:38 PM, Segher Boessenkool wrote:
>>> The LUM signal has an external pullup; everything inside the VIC-II
>>> does pulldown only.
>> Yes... And that pullup is integrated into the RF modulator. Which
>> makes removing the modulator to improve picture quality a pain.
> It is outside of the modulator on the oldest boards.

Yes. But those are very hard to find. There is a replacement circuit 
that was posted in a german forum that works quite well.

>> And here's some other information:
> Interesting stuff. I remember that picture yes.
> It's not clear to me if those measurements all use the same
> external circuitry (like, modulator).

I would assume he used the same board (one for PAL and one for NTSC of 
course) and only switched the VICs, otherwise the pullup in the 
modulator would introduce another variable.

> And there is quite some
> variability between (batches of) chips, so you really need to
> test a bunch of each revision to see if there is really a
> difference :-(

Most people don't have that many...


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Received on 2012-01-13 18:00:33

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