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

Joseph A. Caputo jcaputo1 at comcast.net
Mon Apr 5 10:40:56 EDT 2004


On Saturday 03 April 2004 13:38, The Werpys wrote:
>  James L. Paul wrote:
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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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>
>  I was having trouble like this too, but decided to buy a signal
> amplifier anyway.  It seems to have solve the issue for me.  On a
> side note I did find that one of the connections on the cable
> splitter that went to the cable splitter that was connected to my
> mythbox was not tightly fastened as well. 
>
>  But all in all this did seem to fix the bad singal problem I was
> seeing.


Yes, when I first encoutered this problem my initial thought was that I 
had a poor signal... however I have a signal amplifier & have 
triple-checked my connections... the signal is as good as it's going to 
get.  I suspect it's a combination of the quality of the tuner/
shielding on the card, and the driver/firmware.  Hopefully future 
releases of ivtv will compensate.

-JAC

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