Author Topic: Help with composite video (AVI) horiz / vert centering adjustment  (Read 151 times)

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Offline precaud

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The crt of my Anritsu MS420K VNA will need to be replaced at some point. That is a given.
So I'm looking into LCD replacements.
Internally, the video signal is the ol' composite video, nowadays referred to as AVI. Handily, Anritsu provided a video output jack on the rear panel in case you wanted to use a larger, external crt. The same signal is sent to the internal crt.
So I bought a nice little LCD screen which used to be made by SuperCircuits. It's the right size, has AVI inputs, perfect.

Except - the image is offset vertically up and to the right, enough to clip off the top line of the display.

The SuperCircuits unit has some basic adjustments (bright, contrast, etc) but none for image positioning. I talked to them on the phone, this is a long-discontinued model, they didn't know what to suggest.

I'm a dummy when it comes to video protocols. Is this something that can be adjusted on the source end? The internal crt has adjustments but that doesn't change the video out signal.

Any help/suggestions would be appreciated.
 

Offline Whales

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Re: Help with composite video (AVI) horiz / vert centering adjustment
« Reply #1 on: May 21, 2018, 03:14:12 am »
Any option by the name of 'overscan'?
 

Offline precaud

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Re: Help with composite video (AVI) horiz / vert centering adjustment
« Reply #2 on: May 21, 2018, 03:21:39 am »
Nada. Just brightness, contrast, sharpness, etc. ... nothing that affects the positioning, geometry, size ...
 

Offline precaud

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Re: Help with composite video (AVI) horiz / vert centering adjustment
« Reply #3 on: May 21, 2018, 03:58:07 am »
This is the pcb inside the SuperCircuits. The main IC that handles the video is a TSC7996. I find absolutely no info about this thing.

 

Offline JohnnyMalaria

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Re: Help with composite video (AVI) horiz / vert centering adjustment
« Reply #4 on: May 21, 2018, 11:07:43 am »
I know this is a stretch but bear with me  :)

Have you looked at the signal on a scope to see if the apparent blank space on the left is actually real? Maybe the VNA compensates for this and what you see on the LCD is "true". Maybe it does this deliberately to provide more leeway for adjustment.

Do you have another CRT with composite in (like the 1997 Sony Trinitron that is my primary - and only - TV) or a flat screen TV with composite input to see what they display?

Another thought is that the composite signal is purely for external use and the internal CRT is driven by something else.

See, a stretch...
Tell me it can't be done and I'll do it.
 

Offline helius

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Re: Help with composite video (AVI) horiz / vert centering adjustment
« Reply #5 on: May 21, 2018, 11:58:20 am »
Internally, the video signal is the ol' composite video, nowadays referred to as AVI.
Searching Google for "composite AVI" returns nothing relevant to analog video on the first page.
Searching for "CVBS composite" returns 20 hits that are all relevant.
I think you need to adjust your search terms.
 

Offline precaud

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Re: Help with composite video (AVI) horiz / vert centering adjustment
« Reply #6 on: May 21, 2018, 12:04:38 pm »
I know this is a stretch but bear with me  :)

I'll take a stretch!

Quote
Have you looked at the signal on a scope to see if the apparent blank space on the left is actually real? Maybe the VNA compensates for this and what you see on the LCD is "true". Maybe it does this deliberately to provide more leeway for adjustment.

Do you have another CRT with composite in (like the 1997 Sony Trinitron that is my primary - and only - TV) or a flat screen TV with composite input to see what they display?

Yes, I have used two external crt monitors with it and it works fine with both. No adjustments needed to be made with either one.

The blank space on the left is not a big deal, I can work around that. The upward image shift (and resulting missing top line) is the one I need to solve.

Quote
Another thought is that the composite signal is purely for external use and the internal CRT is driven by something else.

Technically true. But they're assembled from the same signals. They're not combined for the internal crt driver.
 

Offline precaud

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Re: Help with composite video (AVI) horiz / vert centering adjustment
« Reply #7 on: May 21, 2018, 12:06:56 pm »
Internally, the video signal is the ol' composite video, nowadays referred to as AVI.
Searching Google for "composite AVI" returns nothing relevant to analog video on the first page.
Searching for "CVBS composite" returns 20 hits that are all relevant.
I think you need to adjust your search terms.

I wasn't searching for that. I was searching for a data sheet for the TSC7996 video chip.
 


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