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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 26th Mar 2017, 3:40 am   #1
Argus25
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Default Jon Evans (& Peter Brown) 405 line testcard generator

I thought I would have a go at building this generator. A big thumbs up to Jon Evans & Peter Brown for the great job they did on it. Jon's articles are here:

http://www.thevalvepage.com/projects...d/testcard.htm

I have attached a photo of the unit I made, and a screen photo of how one image I loaded to an Eprom appears on my Argus TV. The video from this card is fed to an RF modulator and then to the Argus TV.

I only fell into one pot hole making it: The diagrams show the pin connections for the 74ACT574, but I used the '374 option and they are quite different. After that issue was solved the unit wouldn't run initially as the reset was locked up. Reversing the phase of the clock signal into the 74ACT10 it fixed it. So I figured it must have been because I used a 12MHz clock module and its rising edge must have resulted in a different timing skew than Jon's original clock circuit based on the 74HCU04. Or perhaps the 74HCT4040 ripple counter IC's I used have different overall delays than the ACT types. I found it best in my unit to use the 6Mhz signal from the first ripple counter as the reset circuit's gating pulse. The only other small change was to use an op amp (rather than the two transistors) to help make an output filter to reduce switching noise and transients in the video signal.

(The video signal is actually as sharp as a tack, but its difficult to photograph the VCR97 screen well).

This is a fun project to make and I would recommend it. I'm not sure how many others have built this one, but its well worth it.
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Last edited by Argus25; 26th Mar 2017 at 3:47 am.
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Old 26th Mar 2017, 7:43 am   #2
Cobaltblue
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Default Re: Jon Evans (& Peter Brown) 405 line testcard generator

I built this generator must have been more than 10 years ago now.

I also had the reset problem and had to invert the clock, I used Jon's original clock circuit.

I discussed it with Jon at the time with no firm conclusion.

It's only really fallen into dis-use since I bought an Aurora.

Excellent for home build.

I only used mine with test cards and never loaded pictures.

Cheers

Mike T
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