# Comcast pixelation fix



## ferky1 (May 2, 2002)

I know that this fix has been discussed before, but it took me a long time to find it with so much information on this forum and a pixelation troubleshooting sticky that has almost 1,000 posts. Here's hoping that this standalone post will help people.

The hardware: TivoHD (no upgrades, tweaks or extra hard drives) and Motorolla M-card. Comcast triple play service

The problem: I would get bad pixelation on the same channels around the same times (usually weekday prime time 8-11PM). It always affected the same channels - HD networks, certain digital premiums and several other stations, some digital, some analog. Sometimes it got so bad that I would lose a signal altogether and the screen would go gray on various channels. Diagnostics revealed fluctuating signal strength, usually 30-50 on the pixelating channels, 0 on those that I lost entirely. SNR would skip around between 25-33. Corrected and uncorrected errors were HUGE, moving into the millions if I left the channel on long enough. While this was going on, the majority of my other channels were fine and had signal strength of 80-100 (most had 100), SNR of 36-38 and 0 errors.

Comcast replaced the card a few times, they tested my signal strength and found it more than adequate, they replaced a powered amp that they originally installed. The problem would disappear for days, then come back unexpectedly.

The fix: I was all set to order attenuators based on some luck that people have been having (although they seem to be FIOS people). It didn't make sense to me to attenuate the signal given that my signal reading and SNR on bad channels was already too low. Literally 2 minutes before pushing the order button on a bunch of attenuators, I remembered seeing some posts about diplexers. I happened to have a diplexer in a box of old crap; I have no idea what they do or how I even ended up with one, but I decided to give it a shot. . . .

The fix was immediate. I simply put the diplexer on the line between the wall and the Tivo, while the Tivo was on a badly pixelating NBC. The pixelating stopped, the signal went to 90 and stayed there, SNR stabalized around 37 and errors froze in their tracks. Channels that I had lost altogether reappeared. This was not a coincidence, it was absolutely responding to the diplexer that I put on the cable line.

Like I said, I have absolutely no idea what a diplexer is or does, but this $1.99 peice of metal saved my sanity and probably my relationship with Tivo. I sure hope that the fix is long-term, but my hopes are up.

I hope this post helps someone out there.


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## LDLDL (Jan 12, 2002)

ferky1 said:


> I know that this fix has been discussed before, but it took me a long time to find it with so much information on this forum and a pixelation troubleshooting sticky that has almost 1,000 posts. Here's hoping that this standalone post will help people.
> 
> The hardware: TivoHD (no upgrades, tweaks or extra hard drives) and Motorolla M-card. Comcast triple play service
> 
> ...


Well thank you very much!!!!
I've been having this problem for about a week. I called Comcast and they told me that the problem was with the broadcasted as it was only happening on CBS HD (Channel 233) on all of the televisions in the house, not just on the TiVo. Then I noticed it started happening on Noggin (channel 131).
The problem I'm having with this is why all of a sudden? I've never had pixelation problems on the Comcast hardware.


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## Saxion (Sep 18, 2006)

ferky1 said:


> I have absolutely no idea what a diplexer is


A diplexer is both a passband filter and an attenuator. If you were receiving out-of-band interference in your cable, the filter part helped you. If you needed attenuation, the attenuator part helped you. Either way, this is a great solution to try to cover both possible problems.


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## jlib (Nov 22, 2002)

ferky1 said:


> ...I remembered seeing some posts about diplexers. I happened to have a diplexer in a box of old crap; I have no idea what they do or how I even ended up with one, but I decided to give it a shot. . . .


You probably had a satellite dish in another life, right? Diplexers are usually used to piggy back the connection from a regular antenna on the same coax as the dish so that a separate line does not need to be run.


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## jlib (Nov 22, 2002)

Saxion said:


> A diplexer is both a passband filter and an attenuator. If you were receiving out-of-band interference in your cable, the filter part helped you. If you needed attenuation, the attenuator part helped you. Either way, this is a great solution to try to cover both possible problems.


Just curious, why would a diplexer need to attenuate the signal? Does the oposite diplexer then re-amplify it. I've never used one...

Anyway, ferky1 can determine what is actually helping him by switching to the other port. If it doesn't help then it was the filtering that was the fix.


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## ferky1 (May 2, 2002)

The other port will not pass a signal to the Tivo, so no answer there. I don't know if there is any attenuation going on here because both my signal and SNR actually increased after I used the diplexer; of course, I have absolutely no idea what I'm talking about or what's going on inside that beautif little thing.

I did used to have Satellite, so that must be where it came from.


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## jlib (Nov 22, 2002)

It is as Saxion said then. You were getting out-of-band interference which is now being filtered out.


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## saz25 (Mar 3, 2002)

Hi,
To the original poster: What type of Diagnostics did you run? Does it run on the Tivo? How do you get specific readings on a per channel basis?

Also, where can I get a diplexer? Are there specific types I should look for? Doing a search on ebay finds many that look like splitters.
Thanks,
Steve


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## SCSIRAID (Feb 2, 2003)

jlib said:


> Just curious, why would a diplexer need to attenuate the signal? Does the oposite diplexer then re-amplify it. I've never used one...
> 
> Anyway, ferky1 can determine what is actually helping him by switching to the other port. If it doesn't help then it was the filtering that was the fix.


It doesnt 'need' to attenuate... it just does. Anything that you put in line with the cable has some degree of insertion loss.

Even a simple barrel connector has loss. Here is one that shows .2db of insertion loss.

http://www.trianglecables.com/200-059.html


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## ferky1 (May 2, 2002)

saz25 said:


> Hi,
> To the original poster: What type of Diagnostics did you run? Does it run on the Tivo? How do you get specific readings on a per channel basis?
> 
> Also, where can I get a diplexer? Are there specific types I should look for? Doing a search on ebay finds many that look like splitters.
> ...


In order to view diagnostics, go to the Tivo menu, then (I'm doing this from memory so it may not be exact) Setup and Settings -> System Information -> DVR Diagnostics. The diagnostics screen will show you a TON of information for each channel that the Tivo is tuned to. When analyzing my problem, before going to diagnostics I would put one tuner on a perfectly working channel and the other tuner on a troubled channel. This gave me a good comparison as I worked my way down the diagnostics screen trying to understand all of the information. The information that seemed to differ between working and troubled channels was usually frequency, signal strength, SNR (signal to noise ratio) and corrected and uncorrected errors.

Here is a picture of a diplexer that I stole from a link that TivoCommunity member Subgenious37 was kind enough to post in a different thread (hope he doesn't mind). Mine looks just like this. As you can see, it looks just like a splitter, but has outputs that specify Ant and Sat. Can't tell you if there are different kinds or what kind mine is. A quick web search just showed me tons of places that sell them for less than $10.


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## saz25 (Mar 3, 2002)

Hi,
I just experienced a situation as I'm watching the Celtics on ESPN-HD (849) and for a few seconds there was pixelation and jumpy/sputtering picture. I immediately went into the DVR Diags screen. I saw these numbers:
signal strength 100
SNR 37
corrected and uncorrected are both 0.

Is the signal strength too high? I also noticed the same 100 signal strength on other channels such as CBS-HD.
Any thoughts?
Thanks,
Steve


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