I have an update on my previous article about a cable TV operator trying to make it easy for consumers to receive ClearQAM basic digital channels without a set-top box. He found some Vizio receivers were able to receive only a narrow band of frequencies, not the entire cable TV band. It turns out the frequency range was not the real problem.
I've received a number of e-mail messages from readers about this. First, readers with Vizio DTV sets on cable systems where the proper station major/minor channel number is displayed (example “4.1”) were able to receive ClearQAM signals over the entire band. This pointed to the cable PSIP as the source of the problem.
Recently I heard from the cable operator and also one of his subscribers. The cable operator reported, “After a lot of testing and experimentation, we discovered that the presence of PSIP data on encrypted QAM streams was having an impact how these sets tuned and/or resolved the clear QAM streams. We still don't understand the relationship, but found that more and more ClearQAMs became visible to these sets as we stopped sending PSIP data on other streams.”
The subscriber also contacted Vizio. They suggested a double re-scan (scan once with no connection to the antenna/cable input and scan again with it attached). The subscriber was able to use this to restore the channels, but lost them when the set was powered off and on again. Vizio suggested another technique that apparently does a hard reset on the tuner. This procedure involved unhooking the coax from the antenna/cable input, unplugging the TV set, holding the power button down for 30 seconds while reconnecting power and coax, then doing a re-scan. That, he said, solved the problem.
The cable operator was also making changes to solve the problem, so it isn't clear if this reset or the cable operator's efforts fixed the problem. However, readers may want to keep this reset handy if they run into any channel scanning problems with Vizio DTV sets.