bookman – 4 hours ago  »  Can anything be done to prevent it?

That will depend on what is causing it.

For a starter it is possible that the HD channels are the newer ones to freeview that are broadcast using a weaker signal.

Which HD channels can the problem appear with?

bookman – 18 hours ago  » 

So I’ll try the Maplin filter. Thank you.

Please don’t take my comments as a recommendation. I’m just pointing out I had a similar problem and that solution has worked for me.

Further to Martin’s question, also which channel numbers.

4G, iirc, affects channels 59 and 60 and filters were supplied free of charge, and still are I think, to those affected by the 4G roll-out.

It’d also be useful to know whether the HD recordings actually have the picture/sound break up on the recording itself or whether it is playback. If the recording is rewound is the break up exactly the same?

bookman – 1 hour ago  » 

Replying to Damian, the word ‘channel’ is clearly used in two different senses. The four channels I normally use (BBC1, 2, ITV, 4 (all normally in HD) are all listed as Channel 55.

It is the recording that is faulty. When I select it to play, I get a message ‘Recording failed’ and an option to play anyway. Since by then the programme is past,I click to play anyway and hope that the interruption will be very brief. Sometimes it is, sometimes not.

Causes all sorts of confusion.

Channel 55 is the UHF carrier signal used to transmit the HD Multiplex (Centre Frequency 746MHz).

http://www.digitalspy.co.uk/tech/information/a12613/uhf-channel-and-frequency-guide.html#~p3wcObyIBjwhMO

The channel numbers you enter to view the channels (eg 119 for ITV HD), are more correctly called logical channel numbers, usually abbreviated to lcn.

bookman – 3 hours ago  » 

It is the recording that is faulty. When I select it to play, I get a message ‘Recording failed’ and an option to play anyway. Since by then the programme is past,I click to play anyway and hope that the interruption will be very brief. Sometimes it is, sometimes not.

thanks for the reply.

I asked about rewind as extremely rarely I’ll get picture/sound break up on play back and when rewound it’s fine so a glitch on playback rather than signal when recorded, also extremely rarely the other way round so a glitch when recording as rewinding and playing shows the same glitch.

A few days ago I was recording two HD channels, flicked over to bbc3 and 4 HD and on both the picture was very wierd sort of two different images super imposed, SD was fine, so presumably some transmitter work going on with com7.

The signal levels look okay at 67 – 68%

I could imagine if you’re recording a HD channel, chase-playing another HD channel, the box is doing something else and a scheduled HD recording starts up that you may get a glitch for a short while.

A factory reset, no format, you’ll lose your schedule so take a note with camera phone or similar, is always worth doing, especially after a software update, if you’re experiencing problems.

I think you need to keep an eye on it and see if there are any patterns. It may be a glitch, the box too busy at times or an indication of premature failure. The difficulty with these boxes is there’s no sensible access to the disk or operating system to run rudimentary tests which leaves us with a back box and trying to second guess until something fails conclusively.

bookman – 16 hours ago  » 

Thank you. Earlier replies have suggested interference to the signal,to be countered with an rf filter. Do you discount that idea?

I don’t discount anything these days.

I’d expect rf interference to be causing problems all the time on live TV and on ‘live’ paused TV, not just the start of a recording on bbc 1 or 2 HD which seems to be the case.

I can’t imagine a filter doing any harm, I’d be pleasantly surprised though if it helped. If the signal strength is 67 – 68% on the HD channels, not only SD, then there really shouldn’t be any problem. 4G as I previously mentioned should only affect mux channels 59 and 60 and Luke’s correct in mentioning harmonics, but on mux channel 55 it should be clear of 4G at least, there maybe other RF, but that should affect live and paused-live/chase-play TV.

I have problems remembering what day it is let alone what may or may not have been happening when a recording took place. There’s always transmitter work, if there’s a defence place nearby or the PM/dignitary is visiting locally you’re going to get interference as they sweep the channels. Years ago everytime the fire engine drove past it’d take over our TV and we could hear the cab radio conversation before the picture broke up. Clearly a big red fire engine can’t be missed, other interference might take a while to spot if at all and I don’t understand how it could only affect bbc1+2 HD recordings and nothing else.

Personally I think it’s the box or the disk struggling. Ideally you need do a bit of detective work, make sure exactly which channel and when and what the box was doing, i.e. two recordings or accessing on-demand, copying to usb etc. etc. at that time.

If the disk is struggling then that’s not going to get any better, if you’ve been having power cuts or pulling the plug on the box then that will corrupt the file system.

A proper reboot, i.e. power cycle should be a minimum, personally I’d reset it without format as well.

If over the next few weeks you can’t establish a pattern or put your finger on the problem then maybe a proper format and/or rf-filter as a last resort before returning it if still under warranty. Let us know how you get on