The Humax started to behave erratically and doing a full retune and reformat didn't help (it is running the latest firmware).
Whipped the lid off to wiggle the connectors with little real hope of fixing it, to find an amazing amount of dust inside, not just the accumulations associated with the fan and heat sinks that you might expect, but a uniform layer of very fine dust over the PCBs. It looked like a heavy snowfall, the locations of the surface mount components were barely visible with just the capacitors poking through the surface.
Ten minutes with the cordless Animal (yes I know about static but it was dead otherwise), and to my surprise and pleasure it worked perfectly when reassembled.
In fact the video image is also a bit sharper, so it wasn't only the logic circuits which had been affected.