<div class="gmail_quote">On Sun, Dec 6, 2009 at 7:50 AM, Brian Wood <span dir="ltr"><<a href="mailto:beww@beww.org">beww@beww.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div><div></div><div class="h5">On Sunday 06 December 2009 08:34:17 am Rod Smith wrote:<br>
> On Sunday 06 December 2009 02:12:59 am Greg Zornetzer wrote:<br>
> > Hi all,<br>
> > I recently got an MSI GT 220 512mb card to upgrade my myth box in<br>
> > perparation for 0.22. While the new card does very well with decoding<br>
> > VDPAU, I've noticed a disturbing problem with several of my QAM HDTV<br>
> > signal quality - I see a lot of blockiness (as if the tuner is getting<br>
> > some kind of interference. Removing the GT220 and going back to the<br>
> > motherboard's onboard graphics seems to cure the problem. Does<br>
anyone<br>
> > have advice for some kind of makeshift shield to block interference<br>
from<br>
> > the graphics card? Or other ideas?<br>
> ><br>
> > My tuner card is a Pinnacle 800i (using the latest xc5000 driver) and I'm<br>
> > using 0.21-fixes for right now.<br>
><br>
> I've run into this sort of thing before, but even worse: On my main<br>
> backend/frontend system, a pcHDTV 3000 is next to useless because of<br>
> interference. I tried at least three different video cards in an effort to<br>
> fix the problem. I did find significant differences, but the problem still<br>
> existed with all the video cards I tried. I've never tried a physical<br>
> shield, so I don't know if that would work. I did try moving the tuner to<br>
> different PCI slots, to no avail. It's possible that swapping out the<br>
> video card for another one would improve matters for you, so if nothing<br>
> else you could try removing the video card in favor of another model.<br>
Even<br>
> one from a different manufacturer but based on the same chipset might<br>
be<br>
> an improvement. FWIW, I ended up replacing the pcHDTV 3000 with an<br>
AverTV<br>
> A180. The A180 still has problems sometimes, but not nearly as bad as<br>
the<br>
> pcHDTV. I eventually put the pcHDTV in another computer that functions<br>
as<br>
> a slave backend, and it's flawless in there, so it's definitely not a<br>
> defective card -- it's a defective interaction between the card and other<br>
> components in the backend.<br>
><br>
<br>
</div></div>Not saying it will help, but make sure you have checked all the obvious<br>
things:<br>
<br>
Make sure you have used *all* of the motherboard mounting holes, and<br>
have proper length screws that don't "bottom out" before making a good<br>
contact with the mobo ground plane. I have seen systems where the builder<br>
used only 1 or 2 mounting screws, which can cause problems like you<br>
describe.<br>
<br>
Make sure you are using a good quality PSU, cheaper ones often leave out<br>
de-coupling capacitors and filter inductors, resulting in common mode<br>
interference problems.<br>
<br>
Don't use "modular" PSUs, the connectors can make less-then-perfect<br>
connections, which can cause rectification of high frequency crud if they<br>
behave in a non-linear fashion.<br>
<br>
Make sure all cards are seated properly.<br>
<br>
Dress cables as far away from cards as possible.<br>
<br>
Use a good quality cable from the graphics connector (on mobo or a discreet<br>
card), preferably one that has ferrites on both ends.<br>
<br>
Don't use anything in the case that's not necessary for system operation.<br>
Fancy lights and other "cosmetics" should be avoided.<br>
<br>
Don't use cases with "windows". If you can see the inside of the machine,<br>
stray signals can take the same path as your eyesight. Computing is not a<br>
spectator sport.<br>
<br>
I know these are all obvious things, but they all have caused troubles for<br>
people ignoring them.<br>
<div><div></div><br></div></blockquote><div>Hi Rod and Brian,<br>Rod - I'm at least glad to hear that I'm not the only one. I guess this could be rendered moot by Comcast's impending scrambling of the QAM signals. Either that or I may just have to make a separate myth backend...<br>
<br>Brian, those are some really useful points. Luckily, the computer is a home-build, so I think the motherboard mounting is pretty solid. I don't currently have ferrite cores on my HDMI cables. I'll give that a shot. The case is an Antec HTPC, so it does have some connectors on the front as well as an LCD, but I cannot pull those.<br>
<br>FYI, I found a post on a NZ HTPC board about homebrewing a shield out of plastic-wrapped foil. I tried it with aluminum foil in a plastic sandwich bag - no improvement.<br><br>Thanks,<br>-Greg<br></div></div>