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cmjohnson
Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s
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| Posted: Sun Jun 13, 2010 5:13 am Post subject: Marquee technical question: How does the skew circuit work? |
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I've been reading the Marquee service manual to really learn how it operates and I'm getting a much better overall
understanding of its circuits and how they operate.
But there's one thing that's mentioned in the manual but not explained in any detail, and that's the horizontal skew circuit.
The manual mentions that the convergence yokes east/west coils have accomodations for east/west skew correction but the north/south coils do not have skew correction.
I am simply trying to understand how skew correction is implemented in the convergence coils. I have not yet sacrificed a convergence coil to find out.
I'm GUESSING that there's a second east/west convergence coil pair, offset from the main pair at a different angle, and the two are mixed or phased together to derive a skew signal, but that's probably wrong as there are only four coil connections
to the convergence board. One pair for the N/S coil and one for the E/W coil. Not enough to drive a separate skew coil.
So if anyone knows how this works, please enlighten me. I need to know this because it ties in with my planned
experiment with the G90 focus yokes. That experiment will include trying out G90 deflection yokes, as well, which
have their convergence coils integrated into them. I need to know if or how skew can be implemented with those G90
convergence coils.
CJ
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Sun Jun 13, 2010 4:41 pm Post subject: |
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The EW skew does indeed come from the horizontal convergence coil. Let's say you connect a current of a certain polarity to the h conv coil and the whole image moves to the left. It follows that if the polarity is reversed the image will move right. Start applying the current as the first line at the top is being scanned. Decrease that current, in a linear fashion, to zero when the center line is being scanned. After that point begin increasing the current, in a linear fashion in the opposite polarity, until scanning the bottom line at which time the current is the same value that you started with just the opposite polarity. Repeat. The h skew is just a vertical frequency bipolar current ramp applied to the horizontal converg coils.
Scott
_________________
"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Sun Jun 13, 2010 4:50 pm Post subject: Re: Marquee technical question: How does the skew circuit w |
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| cmjohnson wrote: | I'm GUESSING that there's a second east/west convergence coil pair, offset from the main pair at a different angle, and the two are mixed or phased together to derive a skew signal, but that's probably wrong as there are only four coil connections
to the convergence board. One pair for the N/S coil and one for the E/W coil. Not enough to drive a separate skew coil.
CJ |
The Ultra has vertical Skew as well as Horizontal and uses the same old coil from mid 90's. As Scott explained, it's done electro-magically 
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cmjohnson
Joined: 03 Apr 2006
Posts: 5180
Location: Buried under G90s
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| Posted: Sun Jun 13, 2010 8:38 pm Post subject: |
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Got it! I was thinking that MIGHT be how it was done but it's good to get the answer from the guy who KNOWS.
Thanks, Scott!
This also means that the G90 convergence coils should work with the skew function should I try it as the magic is in the circuitry,
not the coil. Excellent.
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