Tv problem- I have a LG model47lb5800. when I turn on the TV it shows a picture and sound for about 3-10 minutes. The TV then goes black flashes a picture intermittently. What's failing?
I had a similar problem in DEC 2017. Curiously the cable company stopped by in a week or so. (I did not call them for service.) It was a "SPECTRUM" truck and not an "OCEANIC" truck. Apparently Oceanic got bought out and the Technician was going around the neighborhood (Honolulu) searching for "Home Broadcasts" I remember reading about WW2 military was looking for homes with RF signals (looking for spys) I'm a retired Army Signal Corps. The Spectrum tech installed a filter on my cable line to prevent our home from producing stray signals. He also told me that my 'analog' TV won't work in JAN 2018 as they are switching to all digital by then. Says my cable will work for a while but expect the company to switch all the cable boxes out to digital. Sure enough my TV stopped working (on analog channel 3) and my cable box stopped sending the analog signal to my analog set. I found out that some of the other outputs worked (HDMI, Optical, etc.) I got the Bedroom TV (bought 2017) to work on HDMI. Picture is crisp BUT I don't seem to have the picture size right. It's smaller than normal (on analog) and changing screen from normal, wide, zoom, etc. really makes it worse. Panoramic is the best so far. Now I notice our older 'Monitor' 42" Plazma (2010?) still works on Chan 3 analog signal. I didn't have another HDMI ($30) cable so I tried using my old DVD Yellow-White-Red RCA cables and found it did not work.
* So.. Short answer; you need to get your TV hooked up to the HDMI output of the cable box. But I would check with your cable company first to see if they can resolve your issue. Now days, they can use a computer (from their end) to correct the problem or send out a service tech.
PS Try rescanning for channels. You will need channel 3 (sometimes #4) If it shows vertical bars then your set can't tune to the cable box. (Just like the old days of "Outer Limits") They do control the horizontal and vertical. You can try to hook your TV directly to the cable without the cable box to get some of the analog and digital channels if your set is less than 10 years old. But the channels are weird and hard to browse. You will need to write down the channels to remember your favorites. Cable remote won't work. But this is just a short term fix. You will end up subscribing to a cable or internet TV service.