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FIOS TV pixellation fix - attenuate to SNR 31

Discussion in 'TiVo Series3 HDTV DVRs' started by AbMagFab, Nov 19, 2007.

  1. Nov 19, 2007 #1 of 866
    AbMagFab

    AbMagFab What happened, TiVo?

    3,638
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    Feb 5, 2001
    Since I was the first person to post this, and we've since seen this fix nearly everyone who has tried it, I'd like to recommend we sticky this?

    Problem: Pixellation with FIOS TV, usually on a fixed set of channels at a time (often one or two frequencies), but the channel "block" can also sometimes move after a while.

    Why: Since FIOS TV goes from fiber to coax right at your house, there is virtually no signal loss from the source. This means you can have a signal as hot as 10-15db. While this is "within specifications", it appears that it's too hot for the Tivo (more likely, there are other factors that trigger this issue as well, but it's all related to being such a strong, hot signal).

    Symptoms: Other than the obvious pixellation, the most notable objective symptoms are in the Diagnostics screen. Most notably, the "RS Uncorrected" count will skyrocket when on a bad channel. Sometimes it will start at 0 and stay there for a few minutes, but once it gets hit, it just shoots through the roof (like 100's of thousands). RS Corrected will also count up, but that's not really an issue by itself. If you change channels (off the frequency) and then change back, it might stick at 0 for a few minutes, then it will skyrocket again. Sometimes, it's time of day related, where it will be fine at noon, but at 4pm it's skyrocketing again. Often you won't see any problem on the cable box, cable DVR, or TV w/cable card, even at the same time on the same channel.

    Potential fix: It seems that the Tivo tuners are more sensitive than the cable box tuners and even TV tuners with cable cards. While SNR by itself, technically, isn't a fix, it's the best indicator for a fix. On the diagnostics screen, you want to look at the SNR number (not the cable card ones, the tuner ones). Usually this will be in the high 30's. For FIOS TV and Tivo HD/S3, the "magic SNR number" appears to be 31. So you want to attenuate your signal down so that the SNR is 31. Even at 32/33, the pixellation will continue. While you will see your signal strength drop, as long as it stays above ~45, you should be fine.

    Where to buy: You can buy in-line attentuators from a number of places, just do a google search. They are about $2/each, or less in bulk (10 or more). I suggest you get a mixed bag, like a few each of 10db, 6db, and 3db to give you some flexibility in how much you attenuate the signal at each Tivo.

    Installation: Just plug in line, in the coax (they screw in to the coax end). You can do this right before the Tivo (best for testing this fix), or you can do it at the source, and then tweak a little bit at each Tivo (install one more if needed, since cable lengths can cause variable attenuation).

    Non-FIOS problems: While this might work for people without FIOS, it's less likely since this is due to too strong a signal. Most pixellation (IMO) other than this are due to any number of factors, including too weak a signal, dirty hubs between you and the CO, and a bad source signal.


    That's it. This has fixed a dozen or so people since I've posted it and been tracking it, so I think we can officially say this is a fix for at least a good number of people who have tried it.
     
  2. Nov 19, 2007 #2 of 866
    bkdtv

    bkdtv New Member

    7,902
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    Jan 9, 2003
    DC Metro Area
    Repost...

    Steps to Fix

    1. Order a pack of attenuators. These screw on to the end of the coax.

      http://www.smarthome.com/7800.html

      Verizon issues these same attenuators to installers, but most do not know to use them for TiVos.

    2. Find a channel with pixelization.

    3. Once you've found a channel with pixelization, open Settings -> System Information -> Diagnostics. With this screen, you can monitor your SNR and number of RS Corrected and RS Uncorrected errors.

      Your goal is to eliminate the RS Uncorrected errors and the fluctuation in the SNR. A few occasional RS Corrected errors are fine; it is the RS Uncorrected Errors that indicate pixelization.

    4. Disconnect the coax cable from the TiVo.

      Note the process of disconnecting and reconnecting the coax will result in a lot of RS Uncorrected and RS Corrected errors, but don't worry about that. Only worry about errors that increment after the cable is firmly connected.

    5. Most seem to require -10dB to -16dB of new attenuation. A few require as much as -20dB. I would start with -20dB and work your way down.

      Screw one -20dB attenuator onto the end of the coax cable. Then reconnect the coax back to the TiVo.

    6. Is the problem fixed? Wait 60 seconds. Have the RS Uncorrected errors stopped incrementing on the Diagnostics screen?

    7. If not, or you aren't getting a picture, disconnect the coax again and repeat using one -10dB attenuator and one -6dB attenuator.

      Is the problem fixed? Wait 60 seconds. Have the RS Uncorrected errors stopped incrementing on the Diagnostics screen?

    8. If not, disconnect the coax again and repeat using one -10dB attenuator and one -2dB attenuator.

      Is the problem fixed? Wait 60 seconds. Have the RS Uncorrected errors stopped incrementing on the Diagnostics screen?

    9. If not, disconnect the coax again and repeat using a single -10dB attenuator.

      Is the problem fixed? Wait 60 seconds. Have the RS Uncorrected errors stopped incrementing on the Diagnostics screen?

    10. If not, disconnect the coax again and repeat using a single -6dB attenuator.

    11. By now, the problem should be fixed.

    You may want to check a random channel in each QAM block to confirm the problem is eliminated on all channels. I would suggest you test the channels below:

    • one local SD channel (ex: NBC)
    • one local HD channel (ex: CBS-HD)
    • one national SD channel (ex: USA)
    • one national HD channel in the lower QAM block (ex: FOOD-HD or HGTV)
    • one national HD channel in the QAM block (ex: MHD or SHO-HD).
    If you ever see stutter on the Tivo that is not accompanied by RS Uncorrected errors on the Diagnostics screen, that can be fixed with a Settings -> Reboot. I've had the studder issue occur twice since July and a reboot fixed it each time. This issue should be eliminated completely with the next Tivo software update.
     
  3. Dec 5, 2007 #3 of 866
    JonHB

    JonHB New Member

    69
    0
    Aug 27, 2007
    Add me to the list of people that have fixed this problem by using an attenuator.

    I came home tonight and turned on the TV and the channel currently on (KTLADT/805) was severely pixelated. Ahh, perfect opportunity to work on this. Good thing I ordered those attenuators a couple of weeks ago!:p

    I put on a -10 dB and it brought my signal to -31dB. RS uncorrected stopped dead in its tracks! Whoo hoo!!

    Follow the instructions given in the first 2 posts of this thread and you will fix your problem completely.

    Thank you AbMagFab & bkdtv for documenting this so well.
     
  4. Dec 6, 2007 #4 of 866
    litkaj

    litkaj Member

    257
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    Jun 5, 2007
    Exton, PA
    You've got to be careful with this as it's very possible when working top-down that you've fixed a few channels and broken others. Make sure that you check one channel from each frequency.
     
  5. Dec 6, 2007 #5 of 866
    rlawson4

    rlawson4 New Member

    25
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    Nov 27, 2007
    Atlanta,...
    Where do you buy and ATTENUATOR? Do you have a model # so I can see if Amazon has one.
     
  6. Dec 6, 2007 #6 of 866
    bkdtv

    bkdtv New Member

    7,902
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    Jan 9, 2003
    DC Metro Area
    Instructions and order details are in the second post.

    http://www.smarthome.com/7800.html
     
  7. Dec 6, 2007 #7 of 866
    rlawson4

    rlawson4 New Member

    25
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    Nov 27, 2007
    Atlanta,...
    Thank. Much appreciated.
     
  8. Dec 7, 2007 #8 of 866
    joysbox

    joysbox Happy Happy Joy Joy

    161
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    Jun 27, 2003
    Leesburg, VA
    grrr, want to try this, but I only have problems in PLAYBACK mode, I haven't seen any pixilation in live tv. I only really get to see tv about 2 hours a day at best. Any suggestions?
    j
     
  9. Dec 7, 2007 #9 of 866
    richsadams

    richsadams Active Member

    8,893
    2
    Jan 4, 2003
    Nice work AbMagFab and bkdtv. :up: FIOS is coming to our neighborhood soon (buh-bye Comcast). Hopefully things will be fine, but your info will be a good addition to my toolbox in case something comes up.
     
  10. Dec 7, 2007 #10 of 866
    yunlin12

    yunlin12 Tivonation Citizen

    1,223
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    Mar 14, 2003
    San Jose, CA
    Not sure if it applies for FiOS, but is there a signal strength indicator anywhere in your system? I'm on Comcast with hidh speed internet, and if I go to http://192.168.100.1/, I can see a web page served by the cable modem reporting these statistics. Mine says about 34 SNR, and an inbound signal strength of 12dBmV. My electrical engineer gut feeling is that both the signal strength and the SNR need to be tuned correctly to make the receiver work right. I think of the signal strength as a DC signal, and SNR as the AC signal. But without knowing the industry definition for these measurements, it's hard to say what's best.

    Here's a link to AVS post about using cable modem to see signal strength info:
    http://www.avsforum.com/avs-vb/showthread.php?p=12405367#post12405367
     
  11. Dec 7, 2007 #11 of 866
    bkdtv

    bkdtv New Member

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    Jan 9, 2003
    DC Metro Area
    The TiVo or Motorola DVR is the only signal strength indicator.

    Verizon FiOS does not use modems. Fiber connects to the box on the side of your house (or in your basement), and from there you have ethernet output.
     
  12. Dec 8, 2007 #12 of 866
    evlg

    evlg New Member

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    Jun 26, 2002
    Dallas, TX
    How do I know which channels are on a frequency? How many frequencies do I have? Do I just have to try every single channel on the TiVo?
     
  13. Dec 8, 2007 #13 of 866
    bkdtv

    bkdtv New Member

    7,902
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    Jan 9, 2003
    DC Metro Area
    The channels are grouped together as follows:

    National SD channels
    Local SD channels
    Local HD channels
    National HD channels - low (ex: Food HD, HGTV)
    National HD channels - high (ex: MHD, SHO-HD)

    You can check a few channels from each group.
     
  14. Dec 9, 2007 #14 of 866
    AbMagFab

    AbMagFab What happened, TiVo?

    3,638
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    Feb 5, 2001
    Not really. The channels are grouped about 10 per frequency (SD) and 2 per frequency (HD).

    You can see the frequency of the channel on each card on the diagnostics screen.
     
  15. Dec 9, 2007 #15 of 866
    AbMagFab

    AbMagFab What happened, TiVo?

    3,638
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    Feb 5, 2001
    No you don't. I wish you "theory" folks would stay in your own threads.

    If this appears to fix the problem for you (as described quite dramatically by people in this thread), then it's fixed. The problem doesn't move around because of the attenuation.

    Stop spreading FUD, please.
     
  16. Dec 9, 2007 #16 of 866
    AbMagFab

    AbMagFab What happened, TiVo?

    3,638
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    Feb 5, 2001
    It doesn't matter. If you don't notice the problem anymore, it's fixed.
     
  17. Dec 9, 2007 #17 of 866
    bkdtv

    bkdtv New Member

    7,902
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    Jan 9, 2003
    DC Metro Area
    I think you misinterpreted my comment. There isn't likely to be much difference between two adjacent QAM channels, so my suggestion was to check a handful of channels from different blocks. Verizon groups channels in QAM blocks as I indicated above.

    If you were going to check one channel from each block after installing an attenuator, you might check for pixelization (or RS Uncorrected errors) on USA, your local NBC (SD), your local CBS (HD), FOOD-HD, and SHOHD or MHD.
     
  18. Dec 10, 2007 #18 of 866
    jmr50

    jmr50 New Member

    46
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    Dec 27, 2003
    In spite of flushing $50 on AbMagFab's last suggestion for macroblocking problems (the ill-advised just-amp-it idea), I decided to give this one a try, because some of the measurements I'd collected suggested we were overdriving the TiVo. And, thankfully, it actually does seem to have helped the problem - 16dB of attenuation has worked great for 2 weeks now, and still going strong, with no side effects on any channels. If you're sitting on the fence, I can give a resoundingly positive vote. And, it was a cheap fix, too.
     
  19. Dec 10, 2007 #19 of 866
    AbMagFab

    AbMagFab What happened, TiVo?

    3,638
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    Feb 5, 2001
    Nice to see you just throw money at problems without thinking. Glad to help.

    Did you consider doing some problem solving yourself? Naw, that's too gosh darn complicated for you country-folk.

    For what it's worth - amping is a solution for some problems, and attenuation is a solution for other problems. Amazing!
     
  20. Dec 11, 2007 #20 of 866
    FiosUser

    FiosUser Member

    101
    0
    Nov 16, 2007
    I have fixed my Fios + Tivo Series 3 pixelation problem this way.

    I added two 3 and one 8 attenuators to the back of my Tivo. Problem solved. (I had pixelation on TNT and TBS).
     

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