Pixelation and Weak Signal error when signal is known to be good

[drgarner]

I have been using Tablo DVRs for many years. Somewhere along the way my newest Tablo (Tablo Quad TQNS4B-02-CN) started pixelating at random times and would sometimes display the weak signal error when trying to tune a channel. In every case I proved that the signal was fine by connecting the antenna cable directly to the TV or to a USB tuner (Hauppauge). Many others have made this same observation. After many weeks of troubleshooting I decided to do some testing with my old Tablo (Tablo DVR SPVR4-01-NA), aka Tablo 4-Tuner, side-by-side to see if the pixelation occurred at the same time on both. My old Tablo is also a quad tuner.

I connected my antenna cable (via a splitter) to both of my Tablos and powered them up. I used my ATSC DigiAir Pro to measure the signal strength and SNR after the splitter. The readings were excellent. I logged into the “Old Tablo” using the Roku Ultra on my TV. I also logged into the “New Tablo” using Google Chrome on my laptop. (I clicked the red X first to clear all of the Tablo data from the browser.) At this point I am watching the same channel on two devices at the same time using two different Tablos (an old model and new model - both quads and both with hard drives attached). It took about 15 minutes of flipping through channels on both when suddenly, on a channel change, the “New Tablo” started pixelating. The “Old Tablo” continued to display perfectly on the TV!!!. Note that I had adjusted the timeline so that the two displays were in sync to make it easier to correlate any pixelation. This was an exciting find since it proved that the signal from the antenna was still working perfectly as shown on the “Old Tablo” but yet pixelation was visible on the “New Tablo”.

I decided to go one step further to rule out all other variables. I logged out of both Tablos (on the Roku and Chrome on the laptop) - cleared all the sync data - and logged back into the two Tablos in reverse. (The laptop now was displaying the “Old Tablo” and the TV via the Roku was displaying the “New Tablo”). Well, you guessed it - I observed the exact same behavior except reversed. The “New Tablo” (now on the TV) continued to show the pixelation problem and weak signal errors regardless of the device used to display the live TV content.

As an additional test I removed the hard drive from the “New Tablo” and re-ran all of my tests. The results were exactly the same as before - the “New Tablo” continued to display the Weak Signal error at times (when tuning to a new channel) and pixelate at random times. During these errors the “Old Tablo” had no issues at all! I also made sure that every setting was identical between the two Tablos. The only setting that was different was the Tablo Name field under General. The firmware version on each Tablo is the same (v2.2.30).

I also changed out the power supply on the new Tablo. Both power supplies that came with the Tablos are rated at 12V 2A. The DC plugs will not fit interchangeably between the two Tablos but I just happened to have in my junk box a 12V 5A (rated) power supply with a DC plug that fit perfectly. However, nothing changed with my testing results. The new Tablo still pixelated etc at the same time that the old Tablo ran fine.

This puts the final nail in the coffin. This pixelation and weak signal issue is DEFINITELY* a problem in the Tablo firmware or hardware in the Tablo Quad TQNS4B-02-CN. As a tech savvy observer (and engineer) this appears to be an AGC (Automatic Gain Control) issue with the tuner circuitry/firmware. The reason I am posting my experiences is due to the large number of similar complaints which seems to make this a systemic issue instead of an isolated failure with my particular Tablo Quad.

For now I am going to continue using my old Tablo and enjoy an error free Tablo experience. The New Tablo will be relegated to a shelf in the garage. I really wanted to use the new model with the internal hard drive installed.

UPDATE: I wonder if the tuners in the Quad versus the 4-Tuner are more susceptible to overload. My signal is quite strong here (as seen in the DigiAir photo - 85.4 dBuV.). I assumed (I know, I know) that the tuner circuitry/design would be the same but if the Quad is more sensitive to overload that may explain what I am seeing. If the designers adhere to the ATSC specification I would think that the overload threshold would be the same on the Tablo 4-Tuner versus the Quad. I am going to do some further testing with attenuators and let you know the results.

*Pixelation will still occur if the signal really is weak. The signal is strong for this test case.

Hope this helps someone,
Dave G.

[djk44883]

Have had similar struggles myself. With 2 different “platforms”,
Are both on the same firmware versions?
Are both set with the same LiveTV/Recording quality settings?
…all things being equal.

@drgarner

Hope this helps someone,

it may be semantics, The one on the left, aka “Old Tablo” it a Tablo 4-Tuner, “New Tablo” on right is Tablo Quad

[bbaorbb]

I know from experience that a failing hard drive can cause pixelation but I can’t remember if I also got the weak signal message. I’m not familiar with the newer Quad, can you remove the internal HDD and rerun your tests to see if the pixelation only occurs when the HDD is present? If so, then you may have an HDD issue.

[djk44883]

Although the error messages appear straight forward, they can also be somewhat generic - there’s only a few for everything. Non-specific at times

[wfgotblotv]

Excellent write-up! I also have a Quad and am encountering occasional pixelation and weak signal. This includes failed recordings due to weak signal. The Quad itself indicates all channels have 5 green dots for reception. The drive is a brand new 1TB WD Blue HDD.

I’ve been suspecting my antenna, but now I’m wondering if it really is an issue with the Tablo Quad itself.

[ronintexas]

I have both the original 4-tuner model and a quad. They feed 7 TVs throughout the home, as well as tablets, PCs, phones and other devices. I have issues with several channels, although the pixelation occurred on every device (both Tablo DVRs and my TV). I went through many troubleshooting steps (preamp, 4G LTE filters, distribution amps, replacing cables, etc).

The issue I have was related to tropospheric propagation (“skipping”). In the old days of analog signals, when two stations were on the same frequency, you would get “ghosting” (both channels appearing at the same time), but in the digital age, it pixelates, as the signals actually cancel each other out.

This typically occurs in the summer, between 11:00PM and 10:00AM. During this time, through multiple channels scan, I pickup stations from Houston (220 miles away), San Antonio (130 miles away), and stations within the Austin area drop (25-45 miles away). Once the atmospheric conditions clear up, I get the local Austin channels back, without any issues.

BTW - the signal meter on the Tablo is almost useless - not a true indicator of signal strength. Other than a professional meter, there is a mediasonic digital converter that has a good signal strength meter to determine the channel strength. When the tropospheric propagation occurs, the signal for the stations in question will go from 70-80% to “no signal” and back to 70-80% as the conditions happen.

Not much you can do about this. Not sure if this is your problem or not - just wanted to share, as I spent many hours repositioning the antenna, buying products, switching things around, only to find out the reason behind it.

[drgarner]

Yes - the settings and firmware are the same on each Tablo. I edited my post to include this information.

[drgarner]

I removed the hard drive - same problem.

[drgarner]

Your post is unrelated to the issue I described. I did a side-by-side test and the signal from the antenna was fine on the old Tablo and pixelated on the new Tablo. Both were viewed simultaneously. I removed all of the variables. Something is different about the tuners in the Tablo Quad.

[ronintexas]

Did you switch the antenna inputs on the Tablos? (i.e. take the cable off the quad, put it on the 4-tuner, and take the cable from the 4-tuner and put it on the quad)

[drgarner]

Yes, many times. At other times I even connected each Tablo directly to the antenna by itself. In all tests it was the “New Tablo” that pixelated and showed the bogus weak signal error on occasion. For this test one antenna is connected to both Tablos via a 2-way splitter. The cables that connect the splitter to each of the Tablos are 12" long. I connected it this way for the test so I could view both displays at the same time while tuned to the same channel on both Tablos. The signal strength was plenty strong enough that the 2-way splitter made no difference. I adjusted the timelines via a short pause on one Tablo so that the two displays were in perfect sync.

[theuser86]

Maybe you just have a defective unit. Maybe Tablo can take a look at the logs to see if they can tell you exactly why. I assume you’ve already opened a support ticket?

[bbaorbb]

One more avenue to test is the power supply. I’m not sure if both Tablos models use the same model power supply or if they are are rated the same but if they match you could swap power supplies to see if that has any impact. But I agree with @theuser86 that you should contact Tablo support if you have not already done so.

[ronintexas]

Based on what you said, I would say that your quad is defective. I run mine side-by-side, and have never noticed one pixelating more than the other. If one pixelates, so does the other.

[drgarner]

Yes, I did change out the power supply on the new Tablo. Both power supplies that came with the Tablos are rated at 12V 2A. The DC plugs will not fit interchangeably between the two Tablos but I just happened to have in my junk box a 12V 5A (rated) power supply with a DC plug that fit perfectly. However, nothing changed with my testing results., The new Tablo still pixelated etc at the same time that the old Tablo ran fine.

[wfgotblotv]

If you do get in touch with Tablo support, I hope you keep us posted about what you learn! I think you’ve made a very comprehensive case that there might be an issue with the Quad.

[djk44883]

I didn’t save the references, I do know they have different “receiver chips”. I think they’re second generation aka gii / gen2 as the Dual line and use the same as those x 2.

So all things being equal, except the physical tuners, so there are differences. You may/not have found some differences… although unfortunately they may be limited to your situation. Getting them to admit it’s not like you can view your own system logs