Explain this; Signal drop outs between cable box and HDTV

Can someone help me understand this (All working again, but I don't understand why)

1. Cablevision STB connected to LG HDTV via DVI cable. Everything fine for >18 months
2. For no apparent cause, start to get signal dropouts on all stations (picture to black screen to picture. Intermittently. All channels. Sometimes once an hour, sometimes 20 times a minute). However the PS3 had a perfect signal. (Note I swapped DVI inputs and DVI cables. problem stayed with the Cable input)
3. Cablevision comes. They change the box. looks good. They leave. Later I discover that all channels are indeed good except for two channels, which are heavily pixelated (and unwatchable) and a few others lightly pixelated (in the 20's and 30's channel number range)
4. Later, when looking up troubleshooting the TV, I discovered the firmware is updatable, and there is new firmware.
5. Applied the firmware, all channels perfect

Questions
1. What caused the problem in the first place. All was working in (1) above
2. Why did changing the cable box help?
3. If all channels come in on the DVI cable with the same signal, how could it be that only some stations were pixelated with the new cable box
4. What did this firmware do? Its an LG 42LK520

Maybe the cable company made some changes on their end causing the box to not work correctly. New box had new software so worked correctly.

The bad channels... the DVI cable doesn't have much to do with that. It's the transmission from the company to the box. Something was a little different in those channels and your TV didn't like it. Firmware update did something to make the TV ok with those channels.

Of course, that's all supposition with absolutely nothing to back it up.

Me too. But then again I find many things odd.

it's not the TV, it's more likely the signal strength over from the coax, but the only wat to be certain is to know how strong the signal was vs. now, Home Depot does sell a good variety of tools and test equipment for RF

Yes, the signal strength can vary by channel and can be especially noticeable with some high bitrate HD channels depending on what part of the spectrum it's being transmitted on. You're likely seeing the video breakup due to interruptions in the bit stream. SDV makes things even more interesting because sometimes it will work fine, sometimes it won't, depending on what your neighbors are tuned to. The cable tech may not have tested it thoroughly enough. As for the firmware update having an effect, it may have just been coincidence, but there have been some older TVs with HDCP issues with certain cable boxes.

You might also want to check the splitters and amplifiers, if any, in your setup. I actually had an amplifier that was going bad and causing a similar problem for other TVs in the house, not just the ones downstream from it. After I replaced that with a new unit, things improved, though it was still not perfect. It wasn't until I replaced the cheap 4x splitter the previous cable company had put outside with a good amplified splitter, that all the HD channels started working consistently. My internet speeds also started to consistently top out at my capped rate, where it used to jump all over the place and sometimes go out for seconds to minutes at a time.

KuoH

ellory said:   The signal strength on the coax from the street to the STB varies by channel for digital TV? That doesn't sound right to me

And if it true (the cable tech tested the signal and claimed it was fine), how would a firmware upgrade on the TV fix it? (because that would mean the digital signal on the DVI was corrupted)

The fact that the issue did not improve with component cables should be enough to confirm that it's not an issue between the TV and STB. Component is one way only, no handshaking, so it can not have any effect on the STB's ability to display "certain" channels. Hook it up with composite cables and you'll see the same thing. Even using DVI or HDMI cables would not affect the STB's ability to receive channels, though could prevent it from displaying anythin if there's a HDCP compatibility issue. The problem is still between the cable plant and your STB. You can try temporarily hooking the STB directly to the feed from outside the house, bypassing any splitters, and see if the problem clears up. If so, then you may need amplified splitters or something else in your cable wiring is causing interference.

KuoH

ellory said:   Any insight on the DVI STB to TV side there was a problem with only those channels? (Not sure if its relevant, but I also tested with component cables - and the behavior was identical to the DVI behavior(

"Problem cleared up with firmware upgrade on TV. Meaning the problem was not between cable plant and STB"

i think this is just coincidental, since we have to use set top boxes, the TV is reduced to an output device, like a PC monitor/speaker/light bulb.

so it's completely at the mercy of the output of the STB