[Coco] RGB to VGA boards, test equipment needed

[Steve Batson]

I saw Gene's response, seems that he's of the same opinion that the cheap scopes won't cut it.


On Sep 6, 2015, at 4:31 PM, Kandur <k at qdv.pw> wrote:

> Thanks Steve.
> Please read my reply to Gene, where I'll clarify my needs.
> 
> Kandur
> 
> Sunday, September 6, 2015, 1:54:22 PM, you wrote:
>> They say good for audio, which makes sense. Video signals are going to be much
>> used one...if I were to buy one today, I'd want a decent 100mhz Dual Trace
> 
>> On Sep 6, 2015, at 1:19 PM, Kandur <k at qdv.pw> wrote:
>>> Would these pocket oscilloscopes do for checking video signals?
>>> If yes, wich one is better? Are there any others under $100?
>>> http://tinyurl.com/p9jx2ec
>>> http://tinyurl.com/ommymqs
>>> Frida y, September 4, 2015, Barry Nelson among other things wrote,
>>>> At 15khz a .1 uf capacitor has an effective impedance of 106 ohms but at the
>>>> color burst clock frequency of 3.58 mhz, the same capacitor has an impedance
>>>> of 0.444 ohms. Since the CoCo 3's composite video output circuit has a 10 ohm
>>>> resistor on the collector of the output transistor and a 120 ohm resistor on
>>>> the base, putting a .1 uf capacitor from the video output to ground should
>>>> effectively ground out the high frequency color burst signal and part of the
>>>> black and white video, but should leave the horizontal and vertical sync
>>>> pulses virtually untouched. This should eliminate the jitter on the 80 column
>>>> screen. If the capacitor doesn't do it by itself you could a small 10 ohm in
>>>> series. This has the advantage of providing sync as well as a proper black level reference signal.
> 
>>> Thanks,
>>> Kandur
> 
> 
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>>> Coco at maltedmedia.com
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> 
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