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

James L. Paul james at mauibay.net
Sat Apr 17 14:54:53 EDT 2004


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On Friday 02 April 2004 14:27, James L. Paul wrote:
> On Friday 02 April 2004 10:12, Joseph A. Caputo wrote:
> > On Friday 02 April 2004 00:36, James L. Paul wrote:
> > > 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.
> >
> > Yeah, I've found that the unload/reload trick is not reliable for me,
> > either.  It works about every other reload for my 1st M-179, but hardly
> > ever works at all for my 2nd M-179.  I'd love to resolve this as well.
>
> Perhaps this is premature as I only played for a half hour or so last
> night, but it seems so far in my case that switching the card input to
> something else and then back to cable does the trick. It also has the
> advantage of not needing the driver to be unloaded and so doesn't
> significantly disrupt any recordings in progress.
>
> In my case my cable tuner input is 4, so I am now calling something like
> this from cron once a day:
>
> #!/bin/sh
> /in/ivtv/utils/test_ioctl -d /dev/video0 -p 5
> /bin/sleep 2
> /in/ivtv/utils/test_ioctl -d /dev/video0 -p 4
> /in/ivtv/utils/test_ioctl -d /dev/video1 -p 5
> /bin/sleep 2
> /in/ivtv/utils/test_ioctl -d /dev/video1 -p 4
>
> Last night I was watching live output from /dev/video0 while it was
> displaying the problem. As soon as the input was switched back to 4 the
> problem was gone. I was doing a lot of stuff though, and the problem hasn't
> happened again yet so I'm not positive this will always work. Obviously you
> may have to change the input port numbers to appropriate values for your
> hardware (and the command paths), but this is what worked on mine and it's
> what I'm going to test for the next couple weeks instead of reloading the
> driver.

Just an update on this, It's been 2 weeks with the cron job running nightly 
and the problem has not been visible since. For my purposes it seems that 
this workaround works perfectly well.
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