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

[James L. Paul]

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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.

> -JAC
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