[mythtv-users] Stupid S-Video Problem Continues

Brian Wood beww at beww.org
Thu Jun 8 16:37:48 UTC 2006

On Jun 8, 2006, at 10:18 AM, Will Constable wrote:

> Some very helpful suggestions!  I am interested in this idea of  
> tuning the crystals—might not come to that if the card im taking  
> home today does the trick, but I guess this way could save me from  
> having to buy anything short of a few inches kynar wire.  A few  
> questions:
> 1)     Last night I tried putting ceramic magnets near and on the s- 
> video plug to see if this would somehow shield it from weaker  
> oscillating fields generated by the vga cord nearby or the card’s  
> internal electronics.. don’t think it made a difference but I was  
> running up and down the stairs trying to notice the difference as I  
> made changes… not all that reliable.
Ceramic magnets (or any other kind) are unlikely to do anything,  
except perhaps prevent arthritis in your cabling. What you may be  
thinking of is the ferrite beads or "donuts" that are sometimes put  
on cables to choke high-frequency garbage.

Since your interference is from signals in the same frequency range  
as your "desired" signal ferrite is unlikely to work, but you never  
know. Since you are operating in the realm of "wrong engineering"  
anyway, just about any change to your setup *might* help.

> 2)     If I try the crystal trick—first of all, is the crystal  
> (only one of these on the geforce FX board I have on my desk here)  
> a little silver, oval shaped canister with two connections soldered  
> to the board?  If so, I would simply solder a wire to each of the  
> two pins on the back and then experiment with number of twists?   
> Leaving the insulation on, of course…
Yes, that describes what some crystals do look like. They are  
normally labeled "Y" as in "Y1", "Y2", etc., and if there is only one  
it would likely be called Y1, if it is labeled at all.

You have to be careful with modern circuit boards. If the crystal has  
leads that go entirely through the board, or of you have a two-sided  
board, then the pins on the solder side will be connected to the  
crystal, which is a two-terminal device.

If, however, you have a multi-layer board and/or the crystal is  
surface-mounted, then you will have to try and determine where the  
top-layer connections actually go and find connection points that are  
connected to the same points electrically.

You have to be VERY careful with multi-layer boards, and it takes a  
good temp-controlled soldering iron with a precision tip that's well  
kept, and also needs a steady hand. You have to go into such a  
project understanding that there is a fair chance you will destroy  
the board, especially if you are not experienced with such things :-)

In principle trimming a crystal is very simple, but in practice is is  
very easy to damage a board, please exercise extreme care if you  
attempt this.

You might also consider installing a PCI video board for your S-Video  
out, it should be fast enough for SD video and would provide a lot  
more isolation from the VGA.

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