After that slight interruption from @Faust Just for clarification, I'm not "pointlessly trying to avoid an HDD reformat". On the contrary and as the thread title suggests, I'm trying to learn how to understand my symptoms and systematically diagnose where the problem lies. It's really not my intention to challenge the generous advice being offered, but I'm one of those slightly geeky types who kinda needs to know why he's doing something (and I admit, probably over-thinks it). As @prpr advocates, I could just replace all my coax with WF100, and it would certainly improve the system, but if my actual problem is elsewhere it's not going to solve it, nor help anyone with a similar problem. So my understanding at present is that We're agreed that raw signal is within limits The defects occur in both HD and SD transmissions. There is no known pattern when they occur - every minute for 5 mins then nothing for 24 hrs, both during the day and in the evenings. The defects happen while watching both live transmissions and recorded programs. They are not necessarily repeatable on playback; that is, I can have a drop-out of sound while watching a live transmission or a recording; then when I skip back I can (but don't always) get the sound in full, or at least more of the sound than at first time through. Symptoms only occur on HDMI cable, and disappear completely when using Scart or RCA video & audio connections. I'll happily do a factory reset with or without a HDD format if that is next on the troubleshooting list but my curiosity immediately asks questions like: What is the reset designed to do which may eliminate these symptoms? It seems a bit counter-intuitive that HDD faults cause a problem watching a live transmission? Why does the problem only occur through HDMI cable? If it's not a problem with the cable itself (I've tried 2) what processing route within the box is common to playback and live. S.