Today I found that I am only receiving HD channels and no SD ones. I only have basic cable (up to channel 22) and no STB. I've got my cable split between a tv with a QAM tuner and an older tv tuner card in my computer that only works with analog. The HD channels work fine on the tv, but all the ad channels on both my tv and computer card are snowy. What's up with this? Any suggestion/thoughts?
If you have HSI only then there would be a trap on the drop preventing the ch 2-22 analog from coming through.
If you have HSI & limited basic, then a different trap would be placed on the drop to prevent the old expanded basic analog channels from coming though. Most of those traps remain even after the removal of the old analog expanded basic channels. These traps do fail and drift, so it could even affect channels from about 54mhz to 216mhz.
It could just be a RF issue with the splitter, coax, fittings including a long center conductor, or a suck out preventing those frequences from coming through. Standard troubleshooting starting at the ground block should be done to check every inch of the coax cabling, splitters & fittings.