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  #16  
Old 03-29-2015, 01:47 PM
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Phil Nelson Phil Nelson is offline
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Okay, I tried scoping the signal with and without the stabilizer. It DOES clearly eliminate that moving demon pip. Here's the un-stabilized signal:



Here's the signal with stabilizer:



"This thing has GOT to work," I told myself. Once again, I hooked up the stabilizer between the cable box and the modulator. Guess what -- it does work, after all !

Don't ask me how I concluded that it didn't work before. Too many cables, not enough brains, probably

Thanks for the advice, anyhow. If I hadn't gotten some encouragement to investigate things further, I probably would have given up and just lived with the problem.

Regards,

Phil Nelson
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  #17  
Old 03-29-2015, 04:39 PM
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Electronic M Electronic M is offline
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Quote:
Originally Posted by Phil Nelson View Post

My video stabilizer is a cheap item, bought several years ago from a company that no longer exists. No chance of getting a schematic for it, and I don't have the skills or equipment to dive in and hotrod this sort of thing bareback. Here is a peek at the board for those who are curious.



Possibly there is some other stabilizer or signal cleaner out there that could eliminate the interference. The question is how to find it?

Phil Nelson
I know you likely don't need to hot rod it now, but here are some no-schematic tips if you need to do so in the future. Most of the interesting stuff happens in those three IC chips...Google their part numbers for datasheets, and read them. The rest of the circuit would appear to be a large transistor for power regulation, and a few random small transistors for gain, impedance matching, and buffer duty, and some passives for bias and signal shaping.
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  #18  
Old 03-29-2015, 08:55 PM
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Quote:
Originally Posted by Phil Nelson View Post

"This thing has GOT to work," I told myself. Once again, I hooked up the stabilizer between the cable box and the modulator. Guess what -- it does work, after all !

...
Regards,

Phil Nelson
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  #19  
Old 03-30-2020, 11:00 PM
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Phil Nelson Phil Nelson is offline
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Here's a 2020 update on the mysterious interference, emailed in by a guy who read about this issue on my website:

"Hi, I can give you a definitive answer on the rising and falling signal you were seeing on some of the cable channels. It is indeed Macrovision (later Rovi) analog copy protection very much like that used on most prerecorded analog video. I formerly worked for a company that made cable DVRs and I often used a Tek VM700T or a TDS3000 scope with the video trigger option to test this particular feature, despite my personal dislike for forms of copy protection.

The signal that was intended to upset the AGC in analog video recording devices was generated within the set-top box and was controlled by some digital status bits transmitted within the video stream of the source material from the network provider and passed through our headend unmodified. The reason it is present on some channels and not others is simply that some TV networks choose to protect their content and others don't. This was around 2010-2013; I'm not sure what the current state of things might be. Hope this clears things up if you had not already figured it out.
"

Executive summary: the interference looked like copy protection because it was copy protection.

Regards,

Phil Nelson
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  #20  
Old 03-31-2020, 09:37 AM
Chip Chester Chip Chester is offline
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A decent scan of the back of that board would be all you need to clone that item... as long as the ICs are still available and are not programmable devices. The rest of the components are bog standard, and cleaning up a scan for limited-run PC boards is pretty straightforward. No schematic required, unless you want to further understand/modify the circuitry...
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