[mythtv-users] new video card causing interference with cable signal

Brian Wood beww at beww.org
Sun Dec 6 15:50:09 UTC 2009

On Sunday 06 December 2009 08:34:17 am Rod Smith wrote:
> On Sunday 06 December 2009 02:12:59 am Greg Zornetzer wrote:
> > Hi all,
> > I recently got an MSI GT 220 512mb card to upgrade my myth box in
> > perparation for 0.22.  While the new card does very well with decoding
> > VDPAU, I've noticed a disturbing problem with several of my QAM HDTV
> > signal quality - I see a lot of blockiness (as if the tuner is getting
> > some kind of interference.  Removing the GT220 and going back to the
> > motherboard's onboard graphics seems to cure the problem.  Does 
> > have advice for some kind of makeshift shield to block interference 
> > the graphics card? Or other ideas?
> >
> > My tuner card is a Pinnacle 800i (using the latest xc5000 driver) and I'm
> > using 0.21-fixes for right now.
> I've run into this sort of thing before, but even worse: On my main
> backend/frontend system, a pcHDTV 3000 is next to useless because of
> interference. I tried at least three different video cards in an effort to
> fix the problem. I did find significant differences, but the problem still
> existed with all the video cards I tried. I've never tried a physical
>  shield, so I don't know if that would work. I did try moving the tuner to
>  different PCI slots, to no avail. It's possible that swapping out the
>  video card for another one would improve matters for you, so if nothing
>  else you could try removing the video card in favor of another model. 
>  one from a different manufacturer but based on the same chipset might 
>  an improvement. FWIW, I ended up replacing the pcHDTV 3000 with an 
>  A180. The A180 still has problems sometimes, but not nearly as bad as 
>  pcHDTV. I eventually put the pcHDTV in another computer that functions 
>  a slave backend, and it's flawless in there, so it's definitely not a
>  defective card -- it's a defective interaction between the card and other
>  components in the backend.

Not saying it will help, but make sure you have checked all the obvious 

Make sure you have used *all* of the motherboard mounting holes, and 
have proper length screws that don't "bottom out" before making a good 
contact with the mobo ground plane. I have seen systems where the builder 
used only 1 or 2 mounting screws, which can cause problems like you 

Make sure you are using a good quality PSU, cheaper ones often leave out 
de-coupling capacitors and filter inductors, resulting in common mode 
interference problems.

Don't use "modular" PSUs, the connectors can make less-then-perfect 
connections, which can cause rectification of high frequency crud if they 
behave in a non-linear fashion.

Make sure all cards are seated properly.

Dress cables as far away from cards as possible.

Use a good quality cable from the graphics connector (on mobo or a discreet 
card), preferably one that has ferrites on both ends.

Don't use anything in the case that's not necessary for system operation. 
Fancy lights and other "cosmetics" should be avoided.

Don't use cases with "windows". If you can see the inside of the machine, 
stray signals can take the same path as your eyesight. Computing is not a 
spectator sport.

I know these are all obvious things, but they all have caused troubles for 
people ignoring them.

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