Re: VIC-II Sync & Luma signal

From: Rob Clarke <>
Date: Sun, 03 Feb 2013 19:58:39 +0100
Message-ID: <>
On 03/02/2013 19:03, Gerrit Heitsch wrote:
> The luma pin needs a pullup to work. It will only sink current but not 
> supply it. The datasheet specifies a 500 Ohm pullup. The usual circuit 
> also contains a diode (1N4148 for example) between VIC and pullup.
Hmm, I assume the pullup is in the modulator on this board. I just 
powered it on without the vic present and there's nothing pulling it up 
so that could be the problem.
>> What is the minimum requirements a VIC-II needs to generate a sync
>> signal?
> It should do that once you supply power and clock. There will be no 
> picture, but the sync signals should be there. Can be easily seen if 
> you use a real CRT monitor. When you turn on an otherwise dead C64, 
> you still get a twitch from the monitor once it locks onto the sync 
> signal from VIC.
I have a scope so I've been looking at the signal on the pin itself.
> Also, on the 250425:
> - +12V are present at Pin13 of the VIC?
> - Clock signals are present (dot clock and color clock!)?
yep, both
> - Does the board contain any MOS-TTLs? (small ICs with MOS logo
yes, it has a 7711 instead of a 74ls139, a 7712 instead of 74ls08 and 
7708's instead of the dram mux's. Why do you ask?

>   and a 77xx number)
> - Modulator has power? Even if you use the video out, the modulator
>   is needed to convert the video signals into Y/C and CVBS.
I have yet to open the modulator to find out. Certainly the unregulated 
9v is there.


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Received on 2013-02-03 19:00:45

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