[Coco] CoCo2 black and gray video only -- need help!

[Keith Monahan]

Thanks Dave.

I just checked the 6847T1 spec sheet...... Yeah it's saying 3.579535 to 
3.597555. And I'm 3.577817. So I'm out. I was searching for some NTSC 
spec value, but couldn't find it. I guess more important is THIS CHIP 
that's actually consuming the clock is saying it's too low.

https://www.techtravels.org/wp-content/uploads/2021/10/colorburst_annotated.jpg

Is that the crystal there?

The problem isn't so much the cost of the crystal. It's that I have to 
unsolder the whole can to get to it!

Thanks
Keith



On 10/22/2021 11:40 PM, Dave Philipsen wrote:
> The NTSC spec says  +3.579545 MHz ± 0.0003 per cent which is about +/- 10 Hz so you’re quite away off if you’re 1728 Hz slow. From Digi-Key the price of a new crystal is less than a dollar. I bet that it’s just old and has drifted.
> 
> 
> -Dave Philipsen
> 
>> On Oct 22, 2021, at 10:03 PM, Keith Monahan via Coco <coco at maltedmedia.com> wrote:
>>
>> Dave,
>>
>> Thanks much for the reply!
>>
>> I used my scope to sample pin 1, clock output, out of the MC1372P at 2GS/s, in averaging mode, with 64k averages.
>>
>> I'm getting a period of 279.5ns, or 3577817.53 hz. So 1728hz slow. I don't know this stuff that well. Is 1.7khz on the color burst a big deal?