[mythtv-users] PVR250 and static buildup on cable input?

James L. Paul james at mauibay.net
Fri Apr 2 00:36:37 EST 2004


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On Friday 19 March 2004 04:31, Joseph A. Caputo wrote:
> On Friday 19 March 2004 01:55, James L. Paul wrote:
> > On Thursday 18 March 2004 18:29, Steven Marcotte wrote:
> > > Does it kind of look like you are watching TV through a wire pasta
> > > strainer?  That seems to be the PVR250 wierdness that I experience
> > > from time to time.  Sometimes I'll go weeks without any problems,
> > > other times it seems to be a daily occurence.  The problem fixes
> > > itself if I disconnect the cable input or reboot the computer.
> >
> > Yah, that's one way to put it, I have sort of a vertical banding with
> > lines, and oversaturated dropout also. A quick cable
> > disconnect/reconnect of less than a second clears it right up for the
> > next few days or more.
> >
> > > As for a solution to the problem, I think that is in the hands of
> > > the ivtv developers.  They have done a wonderful job so far, its
> > > only a matter of time before the bugs are worked out.
> >
> > Interesting. I wouldn't have suspected this to be an ivtv driver
> > issue. Possibly firmware, but that's the same no matter what driver
> > we use. And I disconnect/reconnect the cable so fast that the driver
> > never drops the stream. Plus, removing and reloading the driver
> > doesn't affect the problem, neither does rebooting the machine. The
> > image problem is persistent until I disconnect the cable input
> > briefly.
> >
> > It is very similar to a problem I've encountered in cable TV signal
> > distribution with a broken coaxial cable. If the cable has a very
> > tiny break or gap in the center conductor, it can still transfer the
> > RF energy even though it's not solidly conducting. Over time static
> > charge can accumulate and result in signal quality changes similar to
> > what I am seeing. I'm ruling this out though because another main
> > effect of this kind of problem is that it gets worse with higher
> > frequencies since the RF energy loss is proportionate to frequency.
> > With the broken cable the higher channels are noticeably worse than
> > the lower channels, and my problem is independent of channel number.
> > Also, if my main input cable was bad, it would more likely affect all
> > my tuners, not just the two PVR250's.
> >
> > I'm actually considering a temporary workaround of putting A/B
> > switches inline to my cards, with the B side disconnected. At least
> > it would make it easier to clear up the signal by not having to
> > fumble with the F-connectors. :) I hate considering such a kludge
> > though.
>
> I had similar symptoms last night... my picture quality on both my
> M-179's had deteriorated; one with oversaturated colors, the other not
> quite as bad, but noticeable.  A reboot didn't help, but unloading/
> reloading the ivtv driver not once, but a couple of times, seemed to
> finally fix the issue.

Just an update after trying the unload/reload driver trick for more than a 
week... It doesn't seem to be reliable. A couple times it worked, a single 
reload cleared up the problem. But a couple times it wouldn't work at all no 
matter how many times I reloaded. In those cases the only fix was to briefly 
unplug the cable from the card input, that cleared it up.

I'd really like to find a solution to this, it's annoying. ;) It's 
embarrassing to have to flip to the backup Tivo to watch a recording.

I think I'll experiment next with switching inputs and generally resetting 
lots of ivtv parameters to see if that somehow knocks the quality back to 
what it should be.

> -JAC
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