Tivo V6 : Channels unavailable

[Caversham51]

For some weeks now we have had an intermittent problem with thirteen channels being unavailable. Channels affected are 113, 144, 149, 170, 287, 288, 306, 317, 325, 347, 376, 430 and 838. When the channels are available the picture often breaks up.

When the problem first occurred the engineer replaced our old Tivo box with a V6 box but that didn't solve the problem. The second VM engineer said "there's a lot of it about, head office are planning a software update which should fix it".

A week later it hasn't improved.

Any idea what is causing this and what the solution is?

[gunner45]

The second VM engineer is wrong (and the first as well). What you have is almost certainly a problem on your access network (so local and not nationwide). What's happening is that those 13 channels are multiplexed onto a single digital transport stream, and a problem on your access network, probably a distribution cabinet, is causing degradation of the signals. You need a competent engineer to find out what is causing the problem. This is not unique, it took three attempts to resolve a signal issue I had a couple of years ago.

[Caversham51]

On both occasions the VM engineer plugged the coax cable into his meter and said that the signal was "good".

Is that consistent with your explanation?

[gunner45]

They did the wrong check, testing for power levels - which tells you nothing about whether the signal is usable if it is polluted by noise. Digital TV fails because of poor quality - low MER (Modulation Error Ratio) and and high post‑BER (Bit Error Rate) - not because of low power. You need a third tech to do a proper job, i.e. check MER/BER on the specific QAM carrier frequency for channel 113/144 while the breakup is occurring. Good luck.

[Caversham51]

Thanks for your responses.

[nodrogd]

Agree with gunner45. You no doubt have an SNR issue here. Noise issues are an absolute pain on the older HFC cable systems. Noise can leak in due to bad joints or cabling. Also another common cause is customers DIY wiring alterations which are not shielded to the correct spec. One customers alterations can disrupt the entire network segment, & then it is a massive detection job on VMs part to find the culprit.